So I've been playing this one for a while (24hrs+ multiplayer ~level 12 and over half-way through single player campaign) and it is a fun and competitive game. The single-player campaign has been covered to death in reviews everywhere so I'll skip over that portion apart from saying: It's very cinematic and can be very frustrating (some missions are almost too unique).
As with previous battlefield games, multi-player is where the main game lies. Supporting up to 32 players at a time (pretty easily I might add), and with interesting and varied maps, there is a lot of interesting firefight to be had. There's also a wonderful leveling component to the game (both overall and in individual classes + vehicles in general).
Explanation of the basics
Leveling in each class will give you access to essential class equipment (repair tool for engineer, health kit for medic, etc.), and access to different and better weapons. Overall leveling is much slower, but the rewards can be used by all classes (shotguns, pistols and equipment upgrades). The equipment upgrades seem very powerful, particularly body armor and magnum ammo which are not available until you've reached higher levels. They allow you to kill faster or be killed slower - both of which are pretty nice.
Leveling is primarily accomplished by killing other players and by completing objectives (destroying/defending M-Coms in Rush Mode, capturing/defending flags). You can also score small points in bunches by doing team-friendly support operations (dropping ammo boxes, health kits, sensors and spotting players for your teammates to kill).
There's an interesting learning curve to the game and several different skills essential to your survival and ability to compete.
1. The basics: How to use cover, and shoot effectively to kill. What are the goals and how are they accomplished? How to use the map and spot players/vehicles?
2. The general strategy: How to survive and use different weapons in different situations. Figuring out how to help your team accomplish goals, and prevent the opposite team from achieving theirs.
3. The Maps: Figuring out how to achieve surprise by flanking or just being where the enemy doesn't expect. Where are the kill zones on each map and how do I get around them. Where will the enemy come from?
4. The finer points: Swapping out weapons while in a firefight rather than reloading. Reloading between skirmishes. When to use grenades. Destroying important cover without destroying your own. Using smoke to disrupt snipers.
Then comes mastering all of these different skills and blending them together to make a killing machine.
How does it play?
The detail in the game is amazing. Whether you are dealing with being temporarily deafened by a nearby explosion or you are pumping RPGs into a tank and ducking into cover for reloads, you'll be immersed. The gunshots echo indoors, the snipers shot echoes through the hills a half-second after firing and the bullets whizzing by sound very, very real.
The destructible environment can be breathtaking and challenging to deal with and effective teamwork is rewarded above all. Sneaking a squad behind the enemy's front line can often cause game-winning disruptions, particularly if they're working together and of varied classes.
It's a wild game, but can be very frustrating. Along with being more knowledgeable due to longer play-time (both about maps and strategy, and having honed important skills), higher levels also get equipment bonuses. Emptying a clip into a level 50 who's returning the favor is often a losing proposition for the first 15 levels or so. That isn't to downplay what an advantage experience is. Coming from unexpected angles on targets they aren't expected to attack, often in a pack, good, high level players can single-handedly alter the complexion of a match.
Inexperienced and less skilled players can influence your team in the same way that experienced and excellent players can. It's a team game and being on a weak or strong team often influences your score as much as any actions you normally take. Nothing in the world is more annoying than being revived by a medic who hasn't made sure the area's been cleared after your death and being gunned down by the same guy, from the same place before you can get your bearings. Unless it's the low-level newbie jumping into a tank and driving it behind enemy lines where he hops out and leaves it for the enemy to take.
Lopsided wins and losses happen a lot due to dominant high-level (and high-skill) players. Headsets and teamwork are king, and if you don't use them regularly (as it seems 90% of the PC population does not), you will be at a significant and severe disadvantage against those who do.
It's a game that sometimes rewards spawn camping and some other aspects of cheap play that might be discouraged in other games, but is still fun and challenging in spite of that. Sometimes you'll be frustrated when you go 2-10 in K/D ratio because of that bastard in the tank who keeps hopping out and repairing. Other times, you'll be thrilled when you go 12-3 because you're that bastard dominating and frustrating the other team with your tank. It's definitely one of the most intense and cinematic experiences you'll get for under $20.