As am I. Nothing to be too pessimistic about either; in the end it's just a game - one of many at that.
As I said, there is more than one side to what could be done gameplay-wise regarding the game. From a "1.6" standpoint, or rather a standpoint where you want to maximize the competitive value of the game and raise the skill ceiling, things like the stamina-system would have to be entirely and fundamentally changed. In 1.6, the stamina-approach was about allowing the player to do whatever, but punishing him for not executing it perfectly. He was free to get crazy with the physics, and was only held back by his own mechanical skill limits. In GO, the stamina-approach is the exact opposite. Instead of punishing a player for not being good at the game, they cap the level of skill one can possibly achieve by limiting the freedom of movement. That is developer-paternalism, haha; as if they were afraid that their players (or children to stay in the analogy) hurt themselves trying to jump too far or too high, or too quick or change pace and direction mid-air etc. Just imagine the simplest yet at the same time most important movements in 1.6 on the common maps. The jump through the whole on B @ de_dust2, the quick strafe-jump onto the ladder and from there into mini-pit in front of banana @ de_inferno in order to not be spotted by an AWP, the jump onto red or through the hut-windows or into the vents @ de_nuke, the ladder-control and strafes on de_train, etc. All of these were necessary to even compete at a decent level in 1.6 and despite being the most simple movements, they are still more demanding than anything you have to do in GO.
This also leads to every player ending up at looking the exact bland same upon reaching the skill ceiling of the game and doesn't promote to grow and nourish an individual style of play.
Same goes for the recoil system. In 1.6 the patterns were random and demanded every player to try and find a shooting technique that worked for him and we saw variety and metagames around that because the shooting technique of choice was also very much dependent on your opponent's choice and the situation etc. In GO, there are 2, maybe 3 styles of shooting regardless of your opponent or the situation you encounter him in. So, from a "1.6" standpoint, this would have to be changed aswell. So with wallbanging, bunnyhopping, crouch-jumping, tagging, etc. All of this adds to the pool of skills players can draw from, practice for and experiment with. For example, these mechanics allowed for so many methods of peeking an enemy to exist in the game, whereas in GO there are, again, maybe 2 or 3 found in wiggle, shoulder and jump-peeking.
From a different point of view though, we can accept that 1.6's skill ceiling was practically non-existent and that the game towards 2010 reached the mechanical height of what can be achieved by a player. So GO doesn't necessarily need all these changes because nobody benefits from a pool of skills to draw from as big as an ocean. A limited pool is sufficient, as long as it offers enough variety for a metagame to happen (e.g. there can be a limited amount of skills, but these skills should be dependent on other aspects of the game and therefore offer multiple methods to be pulled off). More precisely speaking, at the moment there is a good amount of skills relevant for the game (aiming, rifle control, game-sense, grenade-placement and movement to a certain degree). The problem is not necessarily that these skills are too easy to master in GO, but that there's too few ways to execute them. Aiming: everybody aims for the head (as can be seen in the HS% difference to 1.6) because there is no tagging and headshots aimpunch people. Rifle control: Everybody sprays, bursts and taps the same way because the patterns are always the same and strafing left and right is the most efficient way to be hard to hit but stay fairly accurate at the same time, whereas crouching is the exact opposite of what it used to be (it used to be: you are easier to hit but are more accurate, now you are just easier to hit, the recoil doesn't change). Game-sense: There are multiple factors that you can draw from to read the game well. One of the most important one being sound. But the sound system in GO is bad. You can't precisely trace people, you can't tell how many people there are, you can't precisely tell what direction they're going, there are bugs where you hear people where there aren't any, there are inconsistencies in the approach to what can be heard and what cannot be heard (bomb or weapon pickup, bomb plant, certain jumps, weapon switching - sometimes you randomly hear stuff like this, sometimes you dont), directional sound is poor, - that's also why there are practically no prefires happening in GO. In 1.6 or Source you used to be able to tell exactly when someone is going to come around a corner when they are running, and prefire perfectly timed shots. In GO, I have never seen that.
Grenade-placement: Whereas the skyboxes allow you to get creative with the grenade placement, so that the skill-"bottom" so to say is fairly high (it takes practice to get good at throwing GO grenades correctly), the skill-ceiling is fairly low once you get the hang of it. 1.6 grenades fit through every pixel of a crack and can be placed perfectly when you master them. I have never once seen a pop-flash onto a short @ de_dust2 in GO as beautifully executed as in 1.6 (golden flashes). Try to place a flashbang in GO so that it explodes mid-air right after passing a corner of a wall - it is too random to consitently be pulled off, and the enemy will always see and turn away from your flashes unless you - and this is why most professionals have to do it this way - throw them straight up into the sky.
Movement: Won't even start on this one. The impact the movement had in 1.6 is incomparable to what movement means for GO. There's the peeker's advantage which demands players to peek a certain way. Baiting an AWP shot is impossible - you have to strafe out and get them using your ridiculous acceleration. In 1.6 to bait an AWP you could strafe-jump around the corner and back again instantly, crouchhop-peek, double-peek, mid-air-stop-peek, and so on.
Bottom line (lol): You are limited as to how you execute the relevant skill aspects, and even without introducing new aspects of skill we used to have in 1.6, there are things to fix to keep GO competitively evolving with its current skill set: Adjust movement values to help peeker's advantage , to create more creativity for peeking (better air-control etc.) and to make the tagging that is in the game already more prevalent, introduce alternate spraying patterns for crouching, increase inaccuracy for acceleration, fix bugs and harmonize the sound system (there has to be deep thought going into what can be heard and what can not, I feel like they just randomly decided for these things to be audible or not), make the grenades more precisely controlable, harmonize the penetration of objects for projectiles (some really thick walls are bangable (inferno graveyard to big pit, mirage catwalk to B appartments), whereas sometimes mere tin plates eat all your shots) and let us at least bang thin walls (such as appartment walls on inferno), get rid of aimpunching because coupled with increased tagging this will make people think more about their aiming process and how they shoot.
These are the major examples of what I think are changes that could help the game reach its competitive potential gameplay-wise even without touching fundamental stuff like someone coming from a purist 1.6 standpoint would suggest.