Regarding vanilla, in my opinion it is almost perfect right now. Gameplay is very simple yet there is strategy and tactics. This is a great feat that is not achieved by many games: being simple yet deep. Like the game of Go. Players who are looking for novelty don't like it, sure, but it is not a reason to break the game for those who like it either. I'm not saying nothing can be added, but it should be done with extreme care.
Grenade launcher may appear to be a bit too strong. It deals the most damage AND blocks path AND is strong even at long range (sometimes) AND allows you to gain momentum AND allows you to control space. However it is also difficult to master, its power depends a lot on the situation, it requires a lot of anticipation, and it is also the most evadable of the weapons. Also, its 10 ammos are depleted quickly if you use it for all its roles at the same time (gaining momentum AND prevent people from following AND doing damage), so it is very interesting strategy-wise because you have to CHOOSE what is the best way to use the weapon RIGHT NOW.
Moreover, it is not bad to have a weapon which is stronger than the others, simply because it makes it more important to control. If all weapons have the same strength, then it does not matter which one you take. If, however, you have a choice between a better weapon guarded by the enemy and a lesser weapon which is safe to take, then this is an interesting decision to make and brings depth to the game.
If you really want to "balance" grenade launcher, here is what I would propose:
- consider its position in maps very carefully, maybe put a little less of them;
- lower its direct damage to 5 instead of 6.
The damage reduction I think is acceptable because right now, when you spam rockets to prevent players from reaching you, you also happen to kill them easily almost for free. So in this situation grenades give you both things you want: control of your opponent's movement AND damage. Control of movement is very interesting and deep and tactical and should be kept at all cost. Lowering damage would be interesting to consider, to give the player a choice between grenades to control enemy's movement, OR other weapons (laser?) to kill him with no movement impeding. This brings MORE CHOICE and is thus good game design. Finally, I propose lowering by ONLY 1 because when balancing stuff, you should always be very careful and do very slight modifications, one at a time. Look at Blizzard and how they balance Starcraft 2. They are very, very careful. If, after weeks of testing, this damage reduction appears to be a good thing and it appears that it could be even reduced to 4, then, and only then it should be tried. Note that I'm talking about the direct damage here, the splash damage and the self damage are totally different stories.
About maps, now, I'm just wondering: what about ctf5? Why is it not played as much as ctf2? I think ctf5 is a great, great map with lots of interesting tactics and strategies. In my opinion, adding new maps won't really change anything, because this ctf5 status shows what those players really want: one map to master, and only one. Personally, I'm the opposite: I only play ctf5, and I don't like ctf2. Maybe if I started to play before ctf5 existed I would prefer ctf2.
About armor now, I like the idea of a powerup which would make your weapon ignore armor. Right now, the only difference between armor and health is that... they are not the same. This is already quite a lot actually, because it means that you have to choose your path depending on your health and armor status; and if at 1 health and 10 armor, you will still die in one hit from some weapons; and maps can balance armor and health differently for some interesting effects. That being said, this powerup would still bring more depth, I think. It could be tested.
About jumppads. I'm not sure. In Quake 3 I did not really like them. Why not though, they could be tried. Anyway I don't think they will "close the gap" between newbies and veterans, as I'm sure they will allow many new tricks, especially thanks to the hook. They would also lower the movement role of the grenade launcher (grenade jumps, vertical or horizontal), which would allow you to keep your grenades for damage. It would effectively give you more grenades! See how subtle balancing is? And it would trivialize the decision between losing health and a grenade to gain momentum where those pads would be put. So, I'm not sure. The good thing about jumppads though is that they are map-dependent, thus they would not break any existing gameplay (i.e. ctf2 - or ctf5 for me ).
Edit: I just did a quick search and it appears that there are much more ctf5 players than ctf2 players online, at least on servers without password. Are ctf2 players playing in secret servers among themselves?
I mainly play CTF5 in public servers. In-game nickname is DON'T PANIC !!