I only jumped on board at the very end of 1.2, so most of my time has been under 1.3 - Pretty much the same experience you'll see everywhere; Levelling to 30 was good fun but after that it was very poor. I got to around 230GS mostly through the help of underground caches, but it still wasn't exactly an enjoyable experience, and the amount of time you had to invest to max builds was way more than I had. Relying on caches for 268 gear was also painfully slow if not impossible to get a build you wanted.
1.4 is like playing a different game so far. Sure, if you're a very experienced player who can spend hours on it you'll likely hit the ceiling too quickly, but for casuals like me it's improved immeasurably. Have only spent a couple of evenings on it since it came out but I've already been able to try more gear set combos than in a month of playing 1.3. I don't need to drop 3 mags into enemies anymore either. And the AI is better, though perhaps a little 'rushy'. I can solo the named enemies in tier 4 and that was with my so-so 1.3 build, the good parts of which were completely nerfed in 1.4. I imagine they will tone back the loot drops a touch so I'd jump on and get whilst the getting is good!