The popularity of any computer game is given a boost if it is well supported by third-party utilities, map editors, and other ancillary products. One of the reasons Doom became so popular was the profusion of third-party map editors that allowed gamers to easily (and not so easily) design their own game levels.
Judging by the veritable tidal wave of utilities released for Quake just a few months after its release, the third-party support for id's latest creation will be no less robust than it was for Doom. Some of the most popular Quake utilities include QuakeSpy 3.2, a utility used to find Quake servers on the Internet; Jon Mavor's awesome Quake editor, THRED; and Ben Williams' QuMa 1.2, a Quake editor that utilizes Windows 95 and DirectX to let you view your favorite Quake levels.
In a similar vein, the Macintosh version of Marathon 2 has a substantial number of utilities available, ranging from Steve Israelson's Pfhorte 2.0a14, which you can use to create and edit Mac Marathon 2 levels; to Michael Hanson's physics-model editor, Alchemist 1.0b3. Another treasure trove of Marathon 2 utilities can be found at the Marathon HyperArchive NorthWest.
Sadly, that same profusion of game editors doesn't extend to the Windows 95 version of Marathon 2. As of this writing, I've yet to come across a single Windows 95-based Marathon 2 utility.
The Windows 95 version of Marathon 2 has next to nothing in the way of support programs, while Quake has more utilities than you can shake a nail gun at. The Mac version of Marathon 2 fares much, much better, which wins points, but that won't help you if you're a Windows 95 user.