What annoyances do you have with the game engine you're modding for?

RTCW: Sucky (udp based) download system, no QVM, map-oriented (0,0,0-aligned) player hitboxes, no bots

entitie count limitation in q3

Quake3 engines and their derivatives: Pre-transformed input and euler angles.  The latter can be changed, somewhat.

UnrealED 3.0 (Buggy Terrain Tool)

Be able to add new anims for the ghoul2 model format. If you want new anims you have to redo everything from scratch.

SoF2: If a client has "Allow Downloads" on and a server has "Allow Downloads" off, then any custom gametypes or skins on the server, whether they're being used or not, will cause the client to fail to connect to the server.
As a result, many servers can't even put customs on the server for "on the fly" usage, because people won't be able to join the server even when the customs aren't running.
It basically defeats the modular gametype system, which is a great idea.

Q3:A
- unoriented hit boxes

SoF2
- lack of external animation support
- separate multi-player / single player code
- not being able to figure out the BONE_ANGLE stuff

Unreal
- messy as #### (Unreal + UT, UT2k3 looks much neater)
- need to sub-class everything unless you redo everything

Since I am a mapper and haven't really dug into any code, i can't really say what the most limiting factors are from a modder's stand point..  But mapping, I can!  

Danijel.K definately hit a point with the max ents problem.  Other annoying things are hitting the many other limitations, such as max_map_lighting, etc..  (I pray that DoomIII will eliminate most of these problems )

Another problem I have is the old grid size.  Quake engines still use grid sizes based off of textures.  Over the last year, I've been experimenting with real world architecture, and the old grid size makes it extremely difficult to convert dimensions read off of a blueprint into GTKradiant.  If grid sizes were structured in feet and inches, this could also be benificial to modelers.. especially if that scale matches the grid size used in 3dsMAX and other modeling programs.  

Aaron "Lifer!" Gilmore
Team Lead, Mapper
Team Reaction

JK2 : The difference in the mapmodel limitations between the single player and multiplayer executable.