Tony Hawk 3 (available for the PlayStation 2, X-Box, GameCube, and PC, along with a Playstation version that's similar but not quite, see HurtfulPotato's w/u) is a vast game. A complete description is more suited to a FAQ, so I'll only be covering two specific parts of the Tony Hawk 3 experience.
1.Basic Premise (for those who haven't played any of the Tony Hawk games before)
2.What's new in Tony Hawk 3 (from the two previous versions)
Tony Hawk 3, just like it's two previous incarnations, is an "extreme skateboarding" game. While there are usually multiple objectives to complete, Tony Hawk 3 is primarily concerned with points. These points are accquired by successfully pulling off tricks. Usually, the longer it takes to pull off a trick, the more points it's worth. Performing individual tricks, however, will get you nowhere fast. These tricks must be linked together, into what is known as a combo. While individual tricks are worth a specific point value, every trick after the first one adds to your multiplier, shown to the right of your score. Two tricks will generate a x2 multiplier, three a x3 multiplier, and so on. Unsuprisingly, this multiplier multiplies (gasp!) the total score of your tricks, dramatically increasing the amount of points you earn if you successfully land the string of manuevers.
And there we have the catch. If you happen to hit ground-level before you pull off your kickflip, or lose your balance on your grind, you bail, and all those points you could've had are lost...in a rather painful-looking manner, I might add.
That's basically the gist of it. I mean, there's a lot more to learn, but that's the (very) basic idea. Now, for you Tony Hawk addicts, er, I mean, veterans, that haven't picked up 3 yet...
What's new in Tony Hawk 3
60 frames per second gameplay - Yes, almost all the ports of the game hiccup at some point, especially the rushed GameCube version, but it's still beautiful to behold. Prepare to cream thy pants if you're used to 30fps Tony Hawk and haven't seen the PS2 version yet. And if you got stuck with one of the Nintendo 64 versions of the older games (which chug along at about 3 frames per second), by George, get ready for a heart attack.
The Revert - Just as Tony Hawk 2 introduced the manual, Tony Hawk 3 brings a "new" move, the Revert. Those of you who have spent far too much time with the franchise will remember that in Tony Hawk 2, you could hit a button (R2 on the PSX version) to slide your board from goofy to regular stance in a smooth, fairly cool-looking motion. This is still doable, but now it has a name and a useful purpose. Basically, as you're coming back down from catching air on a pipe, tapping said button at just the right time makes you do this same board-sliding technique in the middle of coming down the pipe. You then have a small time frame to go into a manual and continue your combo. Yes, continue your combo. You can now pull off sick air tricks, come down, revert, manual, and hop onto something grindable to continue what can develop into one obscene mother of a combo. Oh, and you can go up the other end of a pipe too for more air tricks, but this usually only works once, as you lose a lot of speed doing said revert. After all, it'd just be silly if you could park your rear at a half pipe and revert yourself into some infinite combo until the cows come home. Thankfully, the fine programmers at Neversoft realized this, and so by the second revert, you probably won't even make it up the other end of the half pipe. Grinding's cooler anyway, so nyah. :>
Note: Mabye not infinite, but a healthy combo can apparently be done on a half-pipe. Orpheum says, "...another way you can keep revert combo's going is by using no comply's and fastplants after the revert. Gives you more air when you launch again, and keeps the speed going. I've managed to string together 8 or 9 air combo's, with a revert between each, and get scores over 200,000 for the trick :-) I reckon it's easier than trying to hit a manual straight after the revert too!
Special Manuals/Lip Tricks - Yup, there's now special manuals (crazy stuff, mostly things that defy the laws of physics, but look cool nevertheless), and special lip trick moves, (yes, there was the Burntwist in TH2, but that was the only one) in case you're not happy just pulling off 20-second special grinds for your sick amounts of points.
Bam Margera - Yup, he replaces Burnquist, just like in the PSX title. Who knows why, but he's got one of the most amusing vert special tricks in the game, and I personally don't really care too much about any professional skaters, much less Bob.
Slightly modified Special Meter - What seems like a minor change is actually a very welcome addition. In previous TH titles, as you'll remember, you had to finish your combo before your special meter filled. Now, it fills as you perform tricks, so you can start busting out specials as soon as your first combo, if you keep it running long enough. Nifty.
Network Play - Very hyped, but rarely used (except in the PC version). Supposedly fun, but I currently can't afford a high-bandwidth connection to hook to my PS2, and my friend who owns the PC version can't join online games, even after applying patches, so I'm clueless on this one.
New Soundtrack - As usual, they've rounded up some musical talent to perform while you're working on getting that new high score. Neversoft took the TH2 Punk/Rap/Stuff That's Almost Punk But Not Quite route again, but the results are, on the whole, much more enjoyable. Even some of the rap is catchy, they (thankfully) stayed far, far away from the whole Self Inflated, Look At Me I'm Rich But Let Me Assure You I'm Still A Hardcore Hoodie (c)rap that's been pervading the airwaves lately. Oh, and if anything annoys you, you can turn off any track you want in the playlist under the sound option menu. Heck, the X-Box version can even play tracks you've ripped to it's internal hard drive.
All-in-all, this is a must-have for the Tony Hawk fan (the games, that is...most "real" skateboarders seem to despise this admittedly unrealistic game), and something I'd reccomend for those who need a good new twitch game. For the latter, I say: Welcome to your new addiction. :D