MatFluor's not wrong, but layering is a level of complexity that isn't always totally necessary, and is separate from the question. Implementation is fun and is highly married to the music (ideally the implementation should be considered during the composing process), but more often than a lot of game composers like to admit, we're tasked with "write me a 2 minute loop."
Your question is precisely where a lot of film composers moving into games fail: they don't have a picture to guide them, so their music often runs out of steam or doesn't develop enough. Writing music for games is much more like composing concert music or writing pop songs: structure matters!
Try any of the following and see where it takes you:
-Change keys (but make sure you can get back to the original).
-Write a section of music with an odd number of bars.
-Pick something that you were doing and do the opposite in the next section (broad, I know).
-Write smaller overall -- the big parts seem bigger that way!
-Short breaks that function like a pop song's bridge, or even better, pre-chorus.
-Follow the "second time, second time" rule. When I was a studio musician and we were coming up with an arrangement on the spot, this was always a quick trick to make sure that the second verse didn't run out of steam (and that's always where a song runs out of steam). We would choose something unique to do during the second half of the second verse. It always gave us a nice boost of momentum into the hook. The most overused version of this is to break and play a few hits before going back into the beat -- works like a charm! Sudden staccato sections in game music, especially action tracks, really help drive the energy of a fight during game-play. Be careful not to draw too much attention to the music if it's not warranted, though.
-Speaking of hooks...how's your melody? Can it be better?
Most important, though, is that whatever you do must feel inevitable. The music needs to support itself in much the same way that a good film score feels inseparable from the picture. That sort of strong musical scaffolding is what makes or breaks a game composer, and is hilariously underrated.
Anyways, hope this helps, and good luck!