I hate MW2, I already got 10th Prestige and got bored releveling the shit again.  I'm also tired of being called a faggot constantly on there.
 
I got up to level 30 on UC2 Beta, and I'm level 18 right now on the retail.
 
Am I too far behind, and is it worth going back into? 

I don't have a permanent net connection for my ps3, so I don't get to play as much U2 I as would like, so I'm still only around lv 15, however, the times I have dropped in for a game, I didn't notice that it was too much of an issue. Though I guess you could say I'm probably a bit more casual about the whole thing than most, so you may have a difference experience. One thing I noticed last time though, was that it took a bit longer to get into a game...could just be me though

I tried going back in yesterday, couldn't really get into it, so I played about 5 hours of Modern Warfare 2 

You are never too far behind.  I'm level 37-ish in the online of that game and still using boosters I got in the early teens.  The only later level things I'm using are costumes and taunts.  It's a great game.

Nah you're not too far behind. The good thing about UC2's online perks is that they really aren't that game changing so, a level 40's main difference to a level 18 is really only down to skill. 

I haven't played it much, but at level 10 (I think - it's been a week since I last played) I can hold my own against level 40 dudes.
 
The boosters are useful but don't make you invincible against low level players - skill is more important.

But one thing that everybody seems to be invincible to is your grenades haha

I personally love it more than MW2, it just feels great in everyway, my favorite part has to be pulling, and kicking people off ledges, it puts a smile on my face every time.  

Yeah, pull-downs never get old.  I say you should get back into it.  I too am burned out on MW2 and this is a great way to mix things up.  I like 3rd-person MP, but Gears of War 2 makes my head implode trying to play that broken piece of crap. 
 
Keep in mind: Everyone has grenades and will use them as  a last resort.  So, be careful when gunning people down, good players can toss them at your feet and take you down with them.

I doesn't matter. When I was a level 1, I was already killing people around level 40. Levels don't say anything other than skill.

It's always worth coming back to. If any of you guys ever wanna organize some type of play session, let me know. I'm on anytime I can be.