Personally I loved the first one. It was probably one of my favorite games on this site. And I couldn't wait for the second one to come out. But when it did come out I tried it, beat it, and thought it sucked compared to the first one! I liked how you could add clothes to the guy, but that was the only thing that I did like..
well, comparing in terms of functionality: HL1: launcher has 2 upgrades, E-Rocket 3 charges, parachute's a fire-and-forget thing, visual upgrade is goggles only, a barebone in fact. Platforms exist only up to 4000 feet but the goal is 4500. HL2: 3 upgrades for launcher (IMHO width is unnecessary), 3 upgrades for visual, a magnet (might have a use, but with those multipliers... hum), a fuel sucker which makes the game too easy after a certain point, an upgrade to boost initial speed (comrades... why so expensive?). Platforms are endlessly upwards (good), goal is higher, overall better graphics (I really like that moon background!), and overall bigger numbers on screen (weird but I don't like this). Better precision for multipliers (nice at least), a $0.25 worth launcher (seems okay) and a $10 coin (nice, aha). The "Restart" button is awesome, and HL1 really lacks it. The fuel sucker makes HL2 easy to the highest extent, and it seems that the average platform density is about 4x bigger than in HL1 - yet easier. I think the game is nice and loses in replayability to HL1, although some weaker gamer can do better with HL2, which might attract him to HL1 and/or the site.
I am for HL1 as the winner... and actually HL2 is sometimes tooo dam slow.
I like hedgehog launch 1 best personaly. It was difficult, but not impossible, and the upgrades were well made. HL2 has some items that make it VERY easy, but is larger, because of the moon and mars. They are both fun, but as I previously said, the original HL is the one I enjoy the most!
I enjoyed the original one more. Firetail is right about the instruction needed for the launcher. I was pulling it the wrong way for the longest time on Hedgehog launch 2. I just enjoyed playing the first one more.