Personally I always thought they should have ended the show with the opening salvos of the Romulan War. I thought Enterprise had gotten more on track in the last 2 seasons and thought it deserved a shot at another season. By the 4th season it finally felt more like a prequel. I know Berman and Braga get trashed a lot but I do think they tried to make Enterprise a good show, and you could tell they tried different things with Enterprise. They brought in Manny Coto to shake things up a bit. And season long story arcs are pretty common on TV today. But Enterprise was the first Star Trek show to actually do a serious season long story arc in season 3, then their mini arcs in season 4. I just think in the first 2 seasons they sometimes fell into TNG trap. At times it felt more like a TNG prequel than an original series prequel. And let's be honest, I think all the spin offs took 2 or 3 seasons to really find their footing. The first 2 seasons of TNG and DS9 honestly were a bit uneven and those ended up being great shows in the long run. Voyager also got better as time went on (though I think of all the shows that had the most unexplored potential--I still liked it, but there were some missed opportunities there).