On the note of Delve Deeper, I noticed that Treasures and Tunnels is on GamerGate, and that it works just fine with the "Buy Games not Socks" 5 for $5 bundle copy. The 5 for $5 bundle already came with a Steam key, and three tickets could easily have already earned you the DLC during the Steam Summer Sale, but it might be worth $1 since it's DRM free.
I purchased Frozen Synapse Soundtrack Edition from Gamersgate. It's certainly an original game, using a simultaneous turn system, the likes of which I haven't seen in a very long time, but I can't say I'm at all fond of it. At least not yet, anyway. I'm hoping it'll grow on me. To clarify, the GamersGate version can't be activated on Steam (not that I give a damn). A key is provided that is used solely to create an account to play online. It's not needed for future installation.
In other words, as far as single player goes, the game is totally DRM free, and as far as multiplayer goes, it's simply a login with an account that you paid for. Unfortunately, there doesn't seem to be any form of hotseat or LAN play, which means everyone must buy the game to play together, but all in all it's a very fair way of handling things.
Somebody here said that you could download FLAC and other formats for the soundtrack for the Steam version, but I didn't see any word of that in the sticky on the Steam forum page. Unfortunately, GamersGate provides only the MP3s. I'm not that keen on the music enough to care either way, but I'd have preferred FLAC. Unless it's been resolved today, recipients of gift copies of the soundtrack edition from Steam haven't gotten soundtracks, only the people who bought the bundle.
The GamersGate version includes both the full soundtrack edition (the MP3 download is listed on the download page for the soundtrack edition as an extra) and mac edition to gift. I don't know whether the Steam version lets you launch the game outside of Steam, but that's obviously a non-issue with GamersGate.
Overall, I'd say go with the GamersGate version unless you really like achievements or something. Of course, I'm biased as all hell to the point where I'd say the best perk of the GamersGate version is that Steam doesn't get any money from it. ;)