BBC Bitesize has lots of things my DS has enjoyed; for very early geometry there's this:
http://www.bbc.co.uk/schools/ks1bitesize//numeracy/shapes/index.shtmlI don't see any geometry-only games as such at the next level up (KS2) but there are lots of game-like computer activities (under Teachers for example).
Googling geometry game gave lots of hits, but I don't have experience of anything else that I remember, sorry.
Ah, but: depending how widely you are prepared to interpret "geometry", you might consider
http://fantasticcontraption.com/ , which doesn't teach geometry as such but certainly encourages geometrical thinking.
