The near-future setting may not be as appealing to some as those in past installments but 2142 has it where it counts.
It leaves to say, most people would probably prefer to have a game set in a modern or historical time period but if you can get over the thematic presentation (though I rather like it, personally) you will appreciate what BF:2142 has going on under the hood.
The classes have been slimmed down to just four, although these represent combination of all the kits from past classes, and then some. Assault/Medic, Recon(Sniper)/Spec Ops and Engineer/Anti-Tank have all been consolidated respectively while the Support class remains largely unchanged. While you might first see this stream-lining as downsizing what it does, in fact, is make every one of the fewer classes far more useful in its own right.
Each class starts with very basic kit items though more can be unlocked through ranking up. Some have accused this aspect of the game as unnecessarily tedious and it may be to an extent. It is, however, possible to unlock the full array of weapons for one "sub-class" in a relatively short period of time, and before the granted unlocks begin to become fewer and more far between. This at least will allow players relatively easy access to the items associated with their favored kit.
The squad/commander system smartly introduced in BF:2 has been continued here largely unchanged, though the points system for teamwork-related scoring appears to have been at least marginally expanded and improved upon. Squads also have access to a nifty Battle Net functionality which allows members of the squad to spot and share the location of hostiles in realtime, not unlike the system used in Ghost Recon: Advanced Warfighter. There are also new squad-leader-specific unlockables as well as an EMP pulse for commanders to disable enemy vehicles.
On that note: vehicles, at times the best and worst feature of the series, seem to be relatively comfortable on the battlefields of 2142. An abundance of anti-vehicle countermeasures and the exclusion of spawn point carpet-bombing are a welcome change from BF:2 and previous. Make no mistake, tanks and the new walkers are still forces to be reckoned with but they seem marginally less overpowered and singular than in previous installments.
The maps in 2142 are possibly the game's greatest asset and while there are plenty of servers running the top fan favorites, you aren't stuck with nearly the same sort of monotony the BF:2 server list offers. All of the maps are wonderfully rendered, detailed with plenty of cover and still huge without feeling like just a bunch of empty space between capture points. Far more interesting than most in BF:2's arsenal and the fact that there are plenty of servers with a full rotation helps to dissuade the monotony which begins to creep in after you wind up playing your 1000th consecutive round on Road to Freakin' Jalalabad--though for those so inclined: Camp Gibraltar and Suez Canal have lots of 24/7's.
Ah, and the one big new addition--Titan mode! Though the setup for a Titan map requires little more than swapping flags for missile silos and sicking a pair of huge, warship/transport vessels in the sky, the result can be an interesting alternative to standard Conquest modes. While Titan mode plays out mostly like Conquest you're afforded the opportunity to make a quick or come-from-behind victory by directly assaulting the opposing team's Titan from the inside. This sort of closed-quarters fighting is a bit new to the series and it tends to work questionably as well in practice as in theory but it is something new and can certainly be interesting.
Bottom line: if you're a fan of the series and appreciate the evolution of it, BF:2142 is a great addition to the fold. The gameplay is solid as ever and fresh with a nice gloss of new tweaks and polish while the near-future setting provides a vivid if somewhat esoteric backdrop for the carnage. For $19 bucks bundled with the Northern Strike expansion you'll probably get much more out of this than dropping $30 on BF:2, at least in terms of variety. About 90% of that $30 dollars worth of content is utterly wasted because over half the populated servers only run 3 maps (or 2 of Special Forces) and a bare fraction offer either of the expansions (Euro Forces is especially rare), which is a great disappointment since Armored Fury has some killer maps.
I digress. Battlefield 2142 is a great installment in the series and made of win--buy it.
An aside--All I can say to the complaints in the nature of "the engine is showing its age" is: get over yourself. I for one have been soundly unimpressed with most of what "next gen" gaming has come up with, I really do not care how pretty it looks if it sucks. The engine in BF:2142 is far from ugly and does what it needs to do, that's really all that is necessary.
Additionally, for the allegations of uninspired design and being too derivative of past iterations: why would DICE go out and break a tried and tested formula? Why would you want to buy a Battlefield title in the first place if it... wasn't? The game's design is its appeal, not just some random game mechanic to be thrown about randomly. Even the new Battlefield:Bad Company is adding classic Conquest modes to its bag of tricks because, why? That's why people play Battlefield.
Fact is, the small tweaks made from BF:2 to BF:2142 end up having very meaningful effect on gameplay, without vastly altering it or worse, breaking it entirely; as over-zealous innovation has a knack of doing.
And if you hate Titan mode, don't play it. Much like with Capture the Flag in the older games, Titan mode is an alternative to the standard, not a replacement. The core gameplay of BF and its Conquest mode is alive and in top form in 2142. If that's some kind of sin then I guess its no wonder developers are so keen to err on the side of caution and just put out games that suck to begin with.