Pro - Size
Con - Quality
With the exception of a mirrorless camera with an APS-C sized sensors, the Lumix and Olympus Micro 4/3 cameras have micro 4/3 sensors which are 2 times smaller than a full frame DSLR where an APS-C sized sensor is 1.5 to 1.6 times smaller. The larger your sensor, the bigger your pixels and the better noise handling and usually image quality. There's of course exceptions to this is you compare across generations where technology has improved, but that's the general census.
Pro - Size
Con - Lenses
The amount of lenses out for these systems does not compare with the lenses for long established DSLR brands. You can of course use legacy manual focus glass from other brands with adapters. I bought an Olympus OM-10 film camera with 50 f/1.8 on it and with a $20 adapter, I can use it on my Olympus OM-D. Also, certain brands are compatible, using the same mount. I use a Panasonic Lumix 20 f/1.7 on my Olympus OM-D.
Pro - Size
Con - Size
This is totally up to the person shooting here. Some people may find the smaller size ackwards to use. I find it difficult to use back button autofocus on my OM-D. My Canon 5D MKII fits great in my giant ham hocks.
Pro - Size
Con - Features
Not all of the features are there that are in bigger cameras. Most use contrast detection auto focus which can be less accurate than the AF in a DSLR. However, my OM-D focuses faster than my 5D MKII on most accounts. Most either use an electronic viewfinder or a rear LCD screen as the viewer. The electronics viewfinder does have some neat tricks like the ability to show you what the photo you take is going to look like vs. what you're actually seeing, zoom in on your target when manually focusing, show what's in focus, etc... or even brighten up a dark room. The resolution on these are not as good as viewing a scene with an optical viewfinder and they're sometimes laggy. I feel that this will of course improve over time.
As much as it sounds like I don't like EVIL cameras by my post, I do. The small form factor, detachable lenses, and good quality give me a camera that's way better than your average point and shoot that I can carry everywhere with me as opposed to a 30lb camera bag with a DSLR and my gear. Don't get me wrong, when I absolutely need the best quality or I'm working a job for a client, my heavy gear comes out, but generally when I'm shooting for me or traveling and need to stay light, I bring the Olympus OM-D with me.