In short: it's a lot of fun. If you were looking for a full entry in the R&C universe, you might be disappointed -- this was deliberately made as a cheaper budget title to fill the void between other games from the looks of it and doesn't offer much in the way of a decent story. What's there is cohesive enough to keep the game itself together, but it doesn't move the overall story arc forward at all, and is largely forgettable.
The campaign has a completely different feel than multiplayer does. While the general idea behind the game is a mixture of tower defense and over-the-top weaponry that the Ratchet series is known for, you get get through the majority of the campaign (admittedly only 5 levels plus a boss level) without worrying
too much about the defense part. I made it through the vast majority of the game using barriers and Warmonger turrets and fully upgraded weapons. They worked wonders against the vast majority of enemies. By the time I had finished each level a handful of times there were still turrets/defenses that I hadn't bothered using yet, since I didn't see the point because weapons/ammo were almost always readily available.
Also, if you're looking for ways to extend your SP experience, like every Ratchet & Clank game, the campaign comes with a large selection of Skill Points to try and achieve. They range from the simple "finish each level without losing a generator" to "defeat 250 enemies with <insert-weapon-here>" and "finish the level faster than an Insomniac employee" (most of them aren't difficult, but they can be a mad-rush and change your priorities in the game. To get the "Olympian" skill point for the first level you have to beat it in 10 minutes. To get the "Insomniac Challenge" skill point you have to beat it in 7:23. It's not hard, but there's not a lot of room for error). There's plenty there to keep you occupied if you want to prolong the SP experience, but they do get rather repetitive and don't really offer any tangible reward.
Now, just because you think you're good at the single player doesn't mean you'll be good at multiplayer. That's an entirely different game, and actually was a lot of fun -- although being pitted against someone who is strategically superior than you in every way is rather demoralizing. There were a couple of games that I played where I was absolutely crushed, but managed to use some of the techniques used against me in order to destroy other players later. So I suppose it was a win-win situation.
The basic setup for multiplayer is this:
- Recon
- There are seven weapon stations scattered throughout every map. In order to acquire any weapons beyond your standard Combuster, you have to go forth and take over one of these generators. They also act as your means of collecting bolts to purchase defenses and soldiers -- the more you possess, the more bolts you will receive during the defense stage (see below). This part is spent rushing around the map trying to take over as many weapons stations as possible while making sure you don't lose too many at the same time. It's basically a mad dash all around the map, and can be rather exhilarating if both you and your enemy are trying to take over the same station.
- Squad
- This is where you will spend a bit of time beefing up your defenses, and where the bolts from all the weapons stations you took over start pouring in. Your first priority should be defending your base -- at least some preliminary defenses should always been maintained. This is also where you will purchase troopers to assault their base - you can choose between your basic peons, brawlers, demolition experts, and motherfuckin' tanks. They don't dick around with the last one, although he'll cost you 5000 bolts (which can be a hefty sum if your opponent is good). Spend all of your bolts wisely, and wait for...
- Assault
- This is where you attack your opponent's base and try and destroy their six generators. The more soldiers you send towards them, the better chances you have of defeating them. Also, the better your defenses are set up, the likelihood of your survival increases. Depending on who you are against, this stage can either be a cakewalk or a living nightmare. I fought one guy who just had the bare minimum of defenses and poured all of his money into brawler troops, which my defenses took out easily while I raped his base. Then there was another guy who annihilated all of my weapons stations so severely that I couldn't keep up with reclaiming them, had no money left to defend with, and was destroyed by 6 tanks stomping in one after another. It can either be a nightmare or a dream, but it's always a blast.
Multiplayer was definitely the main focus behind the game, as it's going to be what determines its longevity. It's definitely a rewarding experience, but I unfortunately can see the community for it dying out fairly quickly. If there are more than a handful of people still playing multiplayer this time next year, I would be amazed. It's unfortunate that such a fun experience is probably going to be ignored by a lot of people. Then again, the EU release hasn't hit yet, so maybe there's still hope for it.

I definitely wouldn't mind seeing more of these budget titles from other franchises that don't attempt to be Game of the Year of All Years, and are just about having fun at an affordable price, which Full Frontal Assault nailed perfectly.