From some advice for a friend, looking to travel around the world, asking about cameras for travel.
I always say 'you should by a DSLR', as it's a quantum leap in abilities. The huge resulting change in your photos is worth it. Just know you that it's bulk may mean you don't have it out all the time, even unconsciously. Most likely, if you get one now, you'll carry it everywhere for at least some time and the pictures you'll have the rest of your life will be worth it.
From my own travel experiences: When you're walking around with a big camera and glass around your neck, the weight and size get to be a burden. So does the "I have an expensive camera" factor. I took my DSLR and a powershot with me on my moto trip...ended up using the powershot for 95% of the shots for those reasons. It was a cheaper cam too, so I would take equipment-risky shots...I dropped it a handful of times where my DSLR would have shattered and would hand it to anyone willing to take a shot. (http://www.flickr.com/photos/n8foo/3597617054/) There is also something to be said for having a camera that's easy to 'wear' all day and have ready to fire. With my DSLR setup, I find myself asking 'is this shot worth getting this thing back out?' all the time...and I miss opportunities due to it. Which means, instead of in my sling bag, I carry it around my neck/in my hands constantly, and we're back to the top of this paragraph. I have long considered picking up a G11 (G12 out now w/better low light) as my travel camera for these reasons.
Back to the DSLR - Assuming Canon 550D, I'd look at 3 lenses. The EF-S 18-200 IS, kick ass walkabout lens, I used it on my 7D when I don't know what kind of photos to expect (travel). 11x equivalent zoom so you can get wide shots and then zoom in on that wildlife off in the distance. The EF-S 17-55 2.8 IS is amazing. Nearly all my best shots have been taken with it. It's got L glass but isn't designated L due to the EF-S lineup. Downside is that it's kinda big. If you want that awesome DOF, pick up a Canon 50mm f/1.8 for $99...it's cheap plastic but will take good low light portraits. I personally opted for the Sigma 30mm 1.4 for my fast prime lens, but it was 4x the price.
Micro 4/3 has no viewfinder, suck. It's avail as a sep. accessory on most but then you're about as bulky as a DSLR. The E-P2 is the best of the breed of 4/3 so you can't really go wrong if you do go down that road. I'd be jealous of it. :-) I played with a Sony NEX-5 tonight at Target and I hated it's ergos and electronic focus ring. Shots looked pretty tho. If you're looking seriously at the 4/3 stuff, check the Canon G11/G12, those are amazing cams and have good ergos. The f/2.8 is plenty for low light, coupled with the IS and kick butt sensor (12800 ISO!).
Re: DOF - if you want more DOF, get further away from your subject and use the zoom. It tends to flatten the image but the DOF will be more dramatic than at closer ranges. You probably already know this.
One last comment: one of the best things you can get to make your photography better is a tripod or even a monopod. It'll make you compose your shots, makes them sharper and lets you leave the shutter open longer then 1/30th.
No matter what gear you buy, 'getting better at photography' is the right path.