I’ve heard much good about SS13, though I still have to try it at some point.
As interesting free games, let’s see.
Brogue is a variation on the original Rogue (IIRC, Brian Walker wrote it to replace his lost copy of Rogue at the time).
It’s a pure ASCII-art rogue-like, but with much efforts spent with the interface, making it far smoother to play (and even look at) than you would expect. But make no mistake, it is hard, unforgiving and you will have to think about your moves to beat it.
I’d suggest you to play it a few times, and go to the wiki only
when if you are stuck, to check what objects and enemies exist, and maybe some helpful tips. Or you can do it the hard way and try to discover everything yourself. It will be hard, unforgiving and rewarding for each step closer
Tales of Maj’Eyal is another rogue-like, but at the RPG end of the spectrum. A big world to explore, nice 2d graphics and interesting, well-developed gameplay. IIRC, it begun as a LotR game (ToME meant Tales of Middle-Earth) until they switched to their own world to better fit the gameplay full of magic.
It’s free but apart from the donations, you can also buy it on Steam if you want to give the devs some money and
have the convenience.
Its engine is also available for free, if you want to create your own rogue-likes.
Battle for Wesnoth is a 2d fantasy turn-based game who goes by the philosophy “simple to learn, hard to master and crank-full of content”. IIRC, there is a purchasable mobile version in addition to the free PC version. If you like turn-based games, play this one. It’s pretty, more than complete and of impressive quality.
Also, it has lots of custom campaigns in addition to the official ones, including some with serious changes in gameplay or mechanics, so it’s also quite moddable.
Neptune’s pride 2 : Triton is a browser-based multiplayer 4x that had been purified to the extreme. The mechanics are very simple and let you focus on the meat of the game, diplomacy. In real time mode, ticks happen every hour and cycles every day, so a standard game can last weeks or months (though it won’t take you long each day, thanks to the simple mechanics).
If you don’t believe how surprisingly great it can be, read this, (based on the slightly different first one).
Note, though, that while the game is free, you may want to take a premium account to be with more dedicated players. I don’t have one (yet), and encountered quite a few AFKers in my games - which helped me win each time, so I’m not actually complaining, but after a few game, it may annoy some.
Knytt and Knytt stories (Non-violent 2d platform/exploration, great feeling),
Eversion (Great dissonant 2d platformer, somehow the 8bit version looks better than the HD one, go figure),
Nitronic Rush (Tron-coloured flying car speed-racer, they went professional with Distance next),
Dariush (Play go, it’s good for you),
OpenTTD (for Transport Tycoon Deluxe, I’ve heard it’s great but not played it yet)
and many others that I don’t have in mind for the moment.
I’m so sorry for the time any of you will waste on those.