Love:
- By far the best community out there
- powerfull and flexible shader system
- easy, yet powerfull script language. Option to move to C++ if you want even more.
- flexible plugin system
- rapid prototyping is a piece of cake
- Lots and lots of great updates in the past few months
- Most stable engine i know (Tried Trinigy Vision, Gamebryo, Unreal Engine 2.5, Torque & Torque Advanced, Unity, ShiVa, Lawmaker, C4 . When i comes to stability, GS is way ahead of the others (except for the Unreal Engine, that one is pretty stable, too))
- Licence & Price

Hate:
- Lots of entities on the screen is (of course) a fps killer; instancing would be sweet. You can't use model clusters in all situations.
- No WYSIWYG Editor (yet). I'm really looking forward to GED
- More or less Windows only
- No Web-Player
- People who think there is a "make game button". Because of that i mostly refer to GS as "The Acknex 7 Engine" when talking to others. Sad but true.
- Users like me who always blame conitc for selfmade bugs