Not quite in the same league as Battlefield but a solid alternative.
Frontlines plays like Battlefield but what keeps it original are the classes, in particular the toys that come with each class. The airstrikes, drones, sentry guns are a hoot to mess around and they all feel perfectly balanced.
Battlefield has always encouraged teamwork with medipacks and ammopacks handed out by fellow players. Frontlines doesn't have this option; ammo crates are spread around the maps and your heath automatically regenerates. So you could argue that Battlefield is for teamplayers and Frontlines is best suited for the lone soldier.
The single player campaign in certainly worth playing but only on the hardest setting (which is still easy when compared to online play). Most of the game's achievements are also obtained in the single player game.
The most disappointing aspect of the game is the lack of any rank structure. You just simply play for points and your place on the Leaderboard. This has undoubtably hurt sales of this game. With no rank structure there really isn't anything to work towards.
Overall it looks great, sounds fantastic and is a lot of fun to play online.