This might help you , some observations, i see all game modes well supported in the servers, in Multiplayer there are 10 game modes with varying number slots
1) Ambush...mostly has 0-32 slots but i have seen 0-8 0-12 and 0-24 etc
2) Checkpoint mostly has 0-8 but i saw a few servers with 0-12 0-16 and 1 with 0-32
3) Firefight mostly has 0-32 slots
4) Hunt mostly has 0-8
5) Infiltrate mostly has 0-32
6) occupy mostly has 0-32
7) Push mostly has 0-32
Skirmish mostly has 0-32
9) Strike mostly has 0-32
10)Survival mostly has 0-8
All of these server slots can vary in numbers so where i say for example 0-32 it is not the rule there are servers that are running 8-12-24 etc
There are also other game other options like Co-op mode with 3 game modes
1) Checkpoint
2) Survival
3) Hunt
Co-op also seems to do well with players on servers
We also have a Custom option with a few game modes but with 2 i have not mentioned yet
1) Flashpoint
2) Battle
In custom servers i think you can use weapons that you have customized in the Steam Insurgency workshop, all you have to do is click on anything you fancy and then click "subscribe" and you can get new weapon skins different uniforms, different sights for your weapons and also custom made maps, so this game does give you plenty for the little it has cost, i only paid £5 for mine, hope this helps you .