NOTE: I was going to throw this up on Wednesday but my cable connection went down for two days as soon as I finished it.

Anyways...
I personally like every edition of SR, in one way of another. Some editions are stronger in certain areas than others, but they all have something going for them.
The first SR corebook I bought was the one for SR1, which I got a few years ago. I had been fascinated with the setting since seeing the mini-guide for the SNES game in a Nintendo Power back in the early 90s, so finding this was a treat. I was a bit disappointed to find that the rules entered "basket case" territory, but the setting and back story more than lived up to my expectations. In fact, I would go as far as to say that SR1 "got it" more than any other edition in terms of the setting. It just felt right. It even had some great art in between the sheets (much better than most of the art in later editions of the product). Of course, if you have Alex Ross and Tim Bradstreet working on the same book you kind of have to expect that.
The next core I got was SR3. Finding the first book jogged my memory of the game, so I when out and got the most recent update of the product (at the time). Obviously, the rules were a massive improvement over SR1. Improved combat and magic rules, improved gear, better clarifications and workable rigger rules. The Matrix rules still were in the rubbish bin, but hey. Even with these improvements, I was a little surprised to see how dramatically the "flavor" of the universe had diminished by the time of SR3. Again (like in the case of SR1), the glass was half full and half empty. Except the full part were the rules instead of the setting this time around.
A bit later, around the time SR4 was announced, I got the SR2 core - more out of curiosity than anything else. I found it to be sort of a weird in-between step for SR1 and SR3. The setting had a bit more color than SR3, but not as much as SR1 (and vice-versa for the game's rules). The setting seemed to have a weird flavor in SR2, with sort of an "Earthdawn with rocket launchers"-feel to it. Not that I have a problem with the ED/SR link, in fact I am using quite a bit of it in my campaign presently. But ED and SR are separate games and need to stand on their own right, and not prop each other up.
Of course, as I progressed through the later SR2 sourcebooks I noticed that the game traded the weird feel for SR3's bland style - but I'm not sure that weird to bland was a good change. But SR2 works and I honestly prefer (the somewhat clarified in SR2 & VR1) Matrix v1.0 to the SR3 system of doing things, so I can't complain too much.
And now there's SR4. I'll just go right out and say that I really like the new rules so far. While I’m also a fan of SR3's rules as well (night and day, huh?), they're a bit heavy at times and that slows the game down a lot - a factor that has caused my home campaign a lot of hiccups over the years. SR4 doesn't have that problem, and the less explicit rules make it easier for me to mod my game to my specifications (I tend to really trick out my games). The style of the setting has also gotten back into the SR1 sweet zone a bit, though some SR2 weirdness has crept back in as well.
Only major two problems exist so far in regards to SR4 that keep me from switching over from SR3 presently. The first is that I don't want to start playing until whatever old SR gear that will be converted *is* converted to the new system. This means that I won't be running any games in the system until the last two or three core sourcebooks are released. The second is that there is quite a lot of errata coming out for the new products presently (which isn't a surprise considering that this is a brand new ruleset), and I'll feel a little more comfortable with SR4 when the core is a bit more stabilized.