I do strongly disagree with Mr. Hellfury, but not for the reasons he pointed out above.
While he is correct that the addition of the 1st edition expansions made the game much more complex and convoluted, if you take the core game from the 1st and 2nd edition they are essentially identical in terms of complexity of the gameplay and options available to the player.
The reason that the core 1st edition game is far, far superior to the 2nd edition game is because of the few essential changes that GW made to the mechanics of the game between the editions. In all cases, I contend that the changes were universally terrible.
1) The removal of the turn clock. 1st edition had a turn clock for the marine player but no timer for the stealer player. This put the marine player under intense pressure to finish his turn (as any unused APs were lost when the clock ran out).
This intense pressure is actually what makes me love the game more than anything else. The first time I played Space Hulk I actually felt like I was playing a scene from the movie 'Aliens' because of this pressure. It makes you feel like the stealers are closing in on you and you only have a scant amount of time to make life-or-death decisions. Removing the clock was the worst idea GW ever made.
2) Changing to specialized dice and the reduced power of the Storm Bolter. 1st edition used two basic dice to represent storm bolter shooting. If a marine stood still his first shot at a stealer would kill it on a roll of a '6' (on either dice). If he stood still and fired again, this kill result would increase to a '5+'. If he continued to stand still and fire at the same target he could increase the kill roll all the way down to a '3+'. Of course, this required a marine to basically spend his whole turn firing at a single stealer, but if you really needed to kill one stealer, you could pretty much count on doing it.
For some insane reason with 2nd edition GW included two shooting dice instead of using standard dice. The problem with this, is that it only had three types of results on the die: A 'miss' result (on four sides), a 'moving kill' result (on one side), and a 'standing-still kill' (on one side).
If the marine was moving (or firing his first shot) he could only kill the stealer with the moving kill result (essentially a '6' on a normal die). If the marine player was firing his second or subsequent shot at the same stealer while standing still he could kill the stealer with either a 'moving kill' or 'standing-still kill' result (essentially a '5+' on normal dice).
However, because of the nature of the specialized dice, that is the best result a marine could ever get (a '5+'), meaning that a marine could often spend its entire turn standing still and firing at a single stealer without killing it.
Thus, the basic Storm Bolter marine was made considerably weaker in 2nd edition.
3) The addition of the 'jam' die. 1st edition used a elegant method to represent storm bolters jamming: If a double was rolled on your two dice when firing overwatch shots, the gun jammed. Howver, since GW went with specialized shooting dice in 2nd edition, they now had to include a third 'jam' die that the players had to roll when firing overwatch shots.
So, instead of using two dice to handle all storm bolter shooting, three dice had to be used. . .but only when firing overwatch shots. In terms of simplicity and elegance, clearly the game moved backwards from 1st to 2nd edition in this area.
4) The increased power of the Heavy Flamer. As discussed above, the basic Storm Bolter marine was reduced in power in 2nd edition, this meant that GW had to boost the power of the Heavy Flamer to compensate for this fact (or it could have been the other way around, they wanted to change the flamer rules and they then had to nerf the basic marine to balance things out).
1st edition used a simple single blast to represent the Heavy Flamer and that blast would affect an entire (single) board piece. This system was insanely simple but made for very tough choices on the part of the marine player: If you had to flame the square you wanted to move into, you effectively blocked yourself from moving.
However, these flamer rules also allowed smart stealer players to keep their models spaced out on seperate board sections to reduce the amount of damage that could be inflicted by the flamer. While this tactic was certainly a bit 'gamey', I think it was easily worth the simple and quick rules.
2nd edition allowed flamers to target particular squares (as opposed to entire board sections), and players could choose exactly which squares they wanted to block stealers from moving into (again, instead of an entire board section). This meant that players could use the flamer to block only the portions of a board section they needed, while allowing the marines to continue to move through the un-flamed squares.
These new flamer rules were certainly more complex and difficult for first-time players to get used to.
In the end, the versatile flamer rules coupled with the reduced effectiveness of the storm bolter marines makes the Heavy Flamer marine the absolute key to every mission. If the flamer marine gets killed in 2nd edition, you can pretty much kiss the mission good-bye.
The complexity of the flamer rules are also likely the reason for the removal of the clock (they take a bit more time to resolve than the 1st edition flamer).
So with 2nd edition you have a less elegant shooting system, a more complex flamer, reduced storm bolter marines, an all-important flamer marine, and the loss of an insanely fun turn timer for the marine player. All that comes together to make overall a less-enjoyable game IMHO.
