My wife and I did the 10 day Baltic cruise from Copenhagen to Stockholm. We are not experienced cruisers - we had only been on one short Carnival Ecstasy cruise in 2007. Regent's Explorer provides a far superior experience.
Bottom line: the Explorer is beautiful and the service is top-notch.
Embarkation was initially a little bumpy - we had stayed at a hotel arranged by Regent and rode the 12:10pm bus to the port to discover a really long line. The initial passport check took 40 minutes. After that, the rest of the checkin process went smoothly.
The G2 cabin was large enough for us, but I can see how more experienced cruisers who are used to a larger room might feel a bit cramped. For example, the space between the end of the bed and the wall is pretty narrow and there is no dining table in the cabin. Our particular cabin was aft so note that the balcony does not have see-through railings - instead, a solid waist high wall keeps you from falling overboard. Not a problem per se, but it cuts down the view a tad when you are sitting in a chair.