The explorer series are pretty good little boats-I have a 380x. I've said it before, it's kinda like the pickup truck of the IK world. It'll hold a ton of gear but other than that it does most things well....but nothing great.
It's super-duper comfortable (with the deluxe seats) and really stable, enough so to stand easily. It's also pretty darn durable, don't ask how I know. These things all make it a great fishing IK. The newer ones (with blue tubes) have some upgrades that mine would benefit from like more drain holes. I do really like the option to run the boat wet or dry.
It doesn't track well and is pretty slow on flatwater. It has the tendency to get surfed a little bit in whitewater but it is still up to the task in class III water. I've seen them on the Gauley...but those were probably better paddlers than I.
Now the sport series ones...I have paddled one at the take out when a guy had one. I wouldn't do more than a class 1 float or a lake in one of those. It's just basically a pool toy/coleman type of craft.
When I got mine they were the best deal around and they came with paddles, pump, seats etc. Now other makers (NRS,Aire,RMR) have lowered their ik pricepoint to where they have outcompeted SE....and SE prices even went up last I saw. The exploreres are good boats but I would only buy one at much less than MSRP given current market choices. If I did see a good deal on one, I'd snatch it up.