After you have tweaked your graphics to a comfortable setting, you'll want to setup your config. You'll find the control interface very familiar, and should have no problems there. The built-in buy aliases have changed slightly, while the weapon names for purchasing a gun remain the same, you must precede the weapon name with the "buy" command, for example, "buy m4a1". Just type "buy" in console to list all the weapon aliasing. The autobuy and rebuy feature is also in the game, if that floats your boat.

Another minor config-related change you'll come across is the radar. There is a new command, "cl_radaralpha [x]", that lets you set the transparency level of the radar when cl_radartype is set to "1". This lets you tweak the radar to your liking, but it will never be fully opaque. The good news is that locations on the radar themselves (teammates, the bomb) are fully opaque and very easy to spot in any light level.

The first type are the larger objects that are fully affected by the world around them. Among this class of objects are small crates, buckets, and of course the infamous steel drum. These objects realistically interact with each other, the world, and the player. However, trying to stand on one will result in you clipping through or pushing it out of the way. One thing to note is that you cannot shoot through most of these objects, including the steel drums. Don't worry, they provide little cover at best, and are easily shot out of the way.

The other, smaller, physics objects you'll encounter are mostly there for aesthetics, and while you can shoot them around, they don't react much with the world, you clip right through them.

The physics system as a whole is really just a neat little side-feature that doesn't offer much in the way of gameplay altering changes. I'm sure this will change when it is put to better use in new maps.

Gameplay Changes
There are, however, a number of other gameplay changes you'll want to watch out for in CS: Source. The biggest change being, in my opinion, the crosshair refresh speed. As noted in rizzuh's article (http://csnation.totalgamingnetwork.com/articles.php/article_201/), the crosshair does not behave the same way it did in CS 1.6 when firing a weapon. Here's what's different:

When firing a weapon in Counter-Strike 1.6, your crosshair will expand to represent the loss of control and recoil. The longer you continue firing, the further it expands until it reaches a maximum point of expansion. When you cease firing, your crosshair will shrink back to its normal size, allowing you to easily line up another target in your crosshair and begin firing again. This is also true to Counter-Strike: Source, but with a slight difference. In CS: Source, your crosshair does not smoothly transition back to its original size, instead it seems to shrink back in phases, one size at a time. This process takes a couple seconds longer than CS 1.6, making recoil harder to control.

Grenades
Grenades have received a rather beefy upgrade. First and foremost, Frag Grenades (previously HE Grenades) do much more damage against armored victims than before. In CS 1.6, if you're wearing armor, grenade damage is reduced by 50%. This is not true in CS: Source. While the actual raw damage a grenade does seems to be about the same, the amount absorbed by armor is substantially lower. In fact, armor seems to absorb 15% at best, usually much less.

Frag Grenades aren't unstoppable however, quite the opposite. They no longer damage players though objects or walls. Hiding behind a crate is all it takes to completely shield yourself from the blast. Even so, you'll still definitely want to start putting Frag 'nades to use in CS: Source.

I'm sure you're aware of the upgrades to the Flash and Smoke grenades. Both are much more useful now. A single smoke 'nade can provide pretty decent cover, especially in darker areas. Two smokes and you can go ahead and set up a picnic. If you're a terrorist on dust you'll definitely want to start using smoke grenades to provide cover from the snipers perched above the underpass, or to block off the right flank inside the halls while you rush the bombsite.

Weapons in CS: Source are largely the same as their 1.6 counter-parts. The AWP delay was reduced to be just long enough to prevent quick-switch exploiting, but short enough that it's really not noticeable otherwise. Aside from that, it performs the same, and you shouldn't have any trouble making un-zoomed quick-shots. It should be noted that the reflections in the sniper scopes are purely for looks, and do not reflect other players.

Another cool addition is that silenced weapons have finally been fixed. Your muzzle-flash is now completely invisible if you have your silencer attached. This should give you a bit of an advantage in the darker parts of dust.

Finally, the PARA's rate of fire has been increased, making it slightly more versatile, but recoil is recoil. You will more than likely find the cheaper rifles easier to work with, and more deadly.

The Rest
Sound in the game is overall much more convincing. Stopsound is no longer usable, but ambience is subtle and well done, wonderfully adding to the atmosphere of the environment. One thing you may notice is that footsteps are harder to make out, you'll really have to be paying close attention to pinpoint enemy locations.

The last slick new feature to watch for is damage information outputted to the console when a round is completed. Stats-Me is no longer needed to display damage taken and received. If you're a pub player you will be used to this feature, but the league players among us will find it very informative during matches to know just how much damage they did, and who to get revenge on next round.