Didn't like the whole Suliban/Temporal Cold War/Delphic Expanse arc, there were a few good episodes but as a whole just never really went anywhere. Introduction of species again like the Suliban, Ferengi, Borg etc. was just rehashed none sense.
It should have fitted with what we DO know about the alpha quadrant not just create a whole new idea. Could have used more Tholian/Gorn/Breen story lines. Should have been about gaining allies to help with the Romulan war. Introduction of Klingons later in the series, the odd skirmish with a bird of prey that almost cost them their lives (Kobyashi Maru style)
Never really improved for me, until the last episode where it just seemed like the whole thing was just Riker's fantasy holo deck program
One thing I did like was the use of Zefram Cochrane (James Cromwell). That's about it... Unfortunately.