retroish games:
plasma sky (vertical shooter)
sonic (sonic from genesis updated gfx)
gunslugs (absolutely awesome little platform shooter
Alien Breed (awesome update but i always loved this game)
emus
atarioid and gbaoid are free and look great (i also use my boy for gba emulation)
n64oid (also free) and muopen64plus are both awesome n64 emulators.
my current favorite emu is epsxe for playstation games. there are a few emus so others might be better but ps1 games on my tablet are a lot of fun, not just old favs but many i missed the first time around.
I also love rpg's lately and Symphony of Origins is my fav android classic style rpg so far. Another one that is a blatant rip off of the top down zelda's i like is called Zenonia.
Im not big into fps's on my tablet but there are quite a few ive tried Modern Combat and the Conduit are two off the top of my head, they take up a ton of disk space. Another game off the top of my head that is free is Slenderman, made me jump out of bed one night lol
Another option if your tablet isnt rooted is to get a bluetooth controller or use an old Wiimote. Some games/emu support the Wiimote/bluetooth out of the virtual box, ive tried it, but i am pretty good with the onscreen controls and having an extra joystick is cumbersome for me.
You didnt really say what you liked so i hope something i mentioned helped. Like you i found a great deal on tablet and thought i would use it for reading and videos, but i end up playing a lot games on it, dont just stick to the playstore, download APKINSTALLER and look on other sites, you can find some great games that way which arent on Playstore (for example all the free oid emulators)