I've built a Hexen 2 source port called Hammer of Thyrion. Its a 3d shooter with classes/spells. The original hexen and hexen2 was made by same people as quake and it plays very similar except its has some rpg elements.

Hexen is more demanding with the key bindings so 810 users be able to more fully use all the commands but heres the limited commands binding i put in for maemo buttons :
Menu Key : Next Weap
Zoom Out : Cycle Inventory
Zoom In : Use Inventory
Fullscreen : Attack
Dpad Enter jump

N800/810 Ready2Run version here (12 megs)
N800 mmc1 version here (311 kb)
N8x0 mmc2 version here (311 kb)
770 version here (374 kb)

For mmc versions grab data in zip (11.5 megs) or tar format (12 megs) to extract to mmc. The eventual data (pak) should be in /hexen2/data1 dir but those archives contain that structure so just extract at root.

Also you can buy Hexen 2 for $4.95 on Valve's Steam id games, Quake1 is $9.95, and Quake 2 is $9.95. Note this game is Hexen 2 not the first Hexen. I also would not 'expect' mission packs to work with any of the maemo ports although some might in the future.