I like Boxhead Bounty Hunters. Partly because it was developed with assistance from XGen and partly because of the gameplay. Don't play it much these days.
I haven't played that many of the Boxhead games, but my two favourites are Boxhead: 2Play and Boxhead: The Zombie WArs. I liked 2Play because it had a great co-op and vs. mode multiplayer component tied up with a fun and addicting single player mode. I liked Zombie Wars because it was more of the classic Boxhead formula along with great new weapons. I liked it less than 2Play ,though, as it didn't have any multiplayer. I also thought the arenas weren't as good as the ones in Boxhead: 2Play, the Rooms, and More Rooms as the Zombie Wars ones were just big open grassy spaces with the occasional trees, while the others were way more interesting, with mazes, open spaces, etc. Either way, I LOVE the Boxhead series, and I can't wait for the next one.