Treasure: and I also use Lutris as a (mainly) dosbox-games-not-on-GOG client,
te_lanus: I use it daily, I used to use steam as my gaming frontend on windows, but found I couldn't get it going on Linux as I had it on windows. Found Lutris after someone mentioned it on Reddit, and found it easy to setup, and easy to use. I use it to launch all my games, from Linux games, to wine (using PoL) and emulated (from the a2600 right up to the PSP),
I don't exactly remember how I found Lutris myself, but I think I found it while looking for a linux alternative to D-Fend Reloaded, which is a client for dosbox games on windows. Thus my main use for it, which is the one I already mentioned - I might also use it for the occasional Humble Bundle game coming on a zip file (so that I won't have to go to its folder every time), but most other launchers either I wasn't very interested in (e.g. emulators of early atari consoles), or weren't satisfying in comparison to other software I was already using (e.g. snes9x vs zsnes which I already knew from windows or DGen vs Kega Fusion -the settings weren't easy to reach on the former). There's also DBGL as an alternative to D-Fend on linux, but I found that one needlessly complicated...
And I also don't really use Steam ; never liked its forced updates policy -that one's pretty annoying, especially when it tries to download a large-sized update for a newly-installed retail game -I had this happen to me when I got Empire Total War, and put me off Steam...well, mostly, until I installed it on my windows pc in order to use GOG connect with a bunch of keys from HB, but still I did not download anything, I only redeemed the keys...