I have a 2003 Hepcat. It is the same as the 2004 except that the 2004 has better wheels and disk brakes. Last year I put around 2500 miles on my Hepcat, doing a number of long rides, including 3 double centuries in the California Triple Crown series. If I had to do it over again I'd get another Hepcat. The short wheel base works for me, as does the over-seat steering. One plus of the Hepcat is the normal "rapid fire" shifters, as opposed to the grip shifters, which feel awkward to me.
If you are a large and/or powerful rider I'd suggest that you get the "speed struts" that support the rear of the seat. Me, I am 6'7", 215 lbs, and make enough power to make the bike feel like it was going to fold up. The struts fixed that.
Be aware that this bike will have a mind of its own when climbing at slow speeds. It takes a lot of concentration to keep the thing going in a straight line while doing 3-4 mph up a steep hill. While doing the Knoxville Double Century (outside of Sacramento CA), I spent a lot of the time grinding up the 11-12k feet of climbing. What makes it worthwhile is the 11-12k feet of descending. The bike goes down hills like it is on rails.