Energy basically referred to mana or whatever you want to call it, and managing it correctly was super important in Guild Wars 1, while Guild Wars 2 doesn't have it.
For buffs and debuffs, at least back when I played, I don't remember people building characters completely dedicated to either spreading or removing buffs/debuffs, while that was almost essential in Guild Wars 1. I remember playing a character build that did nothing but debuff opponents that would destroy anyone who's team didn't run debuff removal in a matter of seconds. Likewise, buffs in Guild Wars 1 were incredibly powerful, and you always needed to keep track what enemies have what buffs on them. Looking at Guild Wars 2, it only seems to have 14 Conditions for debuffs (and a lot of them are incredibly similar), while Guild Wars 1 had
all of this as far as debuffs are concerned. Guild Wars 1 also had 10 conditions roughly equivalent to the ones in Guild Wars 2, but even here the conditions from the first game are much more powerful in places (GW2 blind only causes the next attack to miss, while GW1 causes all attacks to miss at 90% chance).
I mean, I never played Guild Wars 2 PvP at a high level, so maybe buffs and debuffs matter a ton there. But I never played Guild Wars 1 at a particularly high level either, and even at low level PvP with random groups, failing to take into account buffs or debuffs would easily lose you the game. Take for instance the debuff Shame, which causes the next spell you cast to fail and lose you a ton of your energy. You better not cast any spells while that's on you.
For skills that require foresight and timing, a lot of skills in Guild Wars 1 were designed to be incredibly powerful if used right, but very bad if used wrong. Take the skill "Protective Spirit", for instance, which makes one party member only take at most 10% of his health on any attack. Use this on an ally that is just about to get hit by an incredibly damaging ability, and you've saved his life. Use it on someone that is being attacked by something that does multiple low damaging hits, and it does nothing. Use it too soon, and it'll just get dispelled. Or Distracting Shot, which disables the spell the enemy is casting for the next 20 seconds. Use this on something crucial, and the opponents are in huge trouble. Use it on something unimportant (or miss the interrupt entirely), and you've done nothing. This is also where baiting came into play, because you really didn't want to use important skills if they could be disabled. I don't remember anything like that from my time playing Guild Wars 2 PvP, while Guild Wars 1 was full of skills like these.
Man, this turned out very long, but I just loved the combat in Guild Wars 1, PvP in particular, and it feels weird to me that people say Guild Wars 2 has better combat just because it added a dodge button.