Before anyone howls at my low rating of this game, going "what's WRONG with you? Doom RULES!! It deserves a 9 or a 10!", rest assured, I love and got near-obsessed with the game for a few years, but I will get to that; first, lets see what comprises this compilation before we get to the low rating...
One thing I am NOT doing, though, is a review of Doom by itself, since this is a compilation cd (mostly). So lets assume you already know the classic FPS game as it is (which probably 90-99% of everyone on this site does), and get onto what is in this as it is:
*the original Doom game, although with some new, added secrets, slightly better graphics (some buildings have different looks/walls [not monsters, though, so breathe a sigh of relief for this NOT being a George Lucas remaking kinda thing]), a few new elements (like a crushing ceiling in one of the later levels that wasn't in the original, the game has to be restarted at level 9, since there's now no way to survive after meeting the Barons on level 8, etc.), and the final level is different, debuting the Cyber Demon, which wasn't in the original
*the sequels of Inferno (not that great, some of it's weird, but it's got some good levels) and Thy Flesh Consumed (which some levels are VERY hard!)
*twenty Master Levels, most of which are pretty good
*Doom 2, which I don't know if there's new/added stuff here, since this was my first experience with the game when I got this compilation in '98, and
*just a few homebrewed levels for both Dooms...over three THOUSAND of them.
That's what lowers the score on this: a lot of the levels don't come anywhere close to capturing the spirit of the Doom games; a lot of times, they seem more like a chore, rather than a joy to go through; however, there's something for everyone here (plus you've got Doom 1 and 2 on here...and the Master Levels...and...).
As far as the bad stuff goes, though, some levels are too easy, then some too impossibly hard unless you have another player with you and/or you have to resort to cheat codes (all the standard ones work, as far as I know, like the God mode, listening to music from other levels, skipping levels, etc.), some you will NEVER figure out on your own (which makes sense to the person who created them how to get through them, but not necessarily to YOU!), so you'll end up getting stuck, backtracking, never finding that key you need, etc., you'll find several of the same levels over and over again as you play over the years, you'll suddenly come upon several co-op, empty levels in a WAD (level) batch when all the others had monsters and all (gee, real good thinking there, guys!) and some WADs just flat out don't work at all (but there's patches you can download at id's web site that I assume will fix the problems; the computer I use to play this isn't mine, so I don't keep it loaded on there). You're probably better off downloading good WAD files from the net, especially since not many people play Doom anymore, they're more into the successors of Quake, Duke Nuke 'Em and Half Life, so chances are they'll have good descriptions of what to expect in a WAD, hopefully increasing the likeliness of getting a decent batch of levels that you'll like.
As far as the good stuff goes, though, occasionally you'll find a really good level, some really big, cool ones that will take a long, happy time to get through, finding either good, original music, or decent music downloaded from somewhere and put in the game, and all kinds of surprises, like one level that has a photo of a topless Asian babe on the wall at one point (heh/yum), funny, replaced sounds with clips from movies and all, some killer co-op and/or deathmatch levels, finding the Doom logo reflected on a ceiling, mixing in enemies of Castle Wolfenstein when it's least expected, etc., etc., etc...plus this will take you a very long time to get through, as I've been going through these levels on and off since the year 2000, and I'm only near the end of the letter D for the Doom II WADs!! So as you can see, I've still got a ways to go, and I more than got my $30 worth years ago.
Compilations like these should be avoided, though, if they have non-professionals making a ton of levels like on this one, unless you're just a glutton for punishment.