Yesterday I ran a beholder encounter, inspired by this image (which is the cover art from Dungeonscape, I think):The difference is in the stunting. In how the terrain is used. In 3.X statting that room up is a largely wasted effort. In 4e it really isn't (although it is probably overkill).
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I'm not sure exactly what the artist intended, but to me it looks as if the central beholder is hovering over a chasm, with uneven rocky surfaces leading up to it (archer on one side, flaming sword guy on the other). I drew up my map similiarly, including with the side tunnel (behind the tiefling) which on my version ran down into the chasm, and the columns, stalactites, etc.
I didn't use four beholders, only 2 - an eye tyrant (MV version) and an eye of flame advanced to 17th level and MM3-ed for damage. And also a 15th level roper from MV, introduced on a whim when the player of the wizard asked, before taking cover behind a column, if it looked suspicious. (Response to result of 28 on the Perception check before adding the +2 bonus for knowing what he is looking for - "Yes, yes it does!")
Anyway, the terrain was pretty awesome. I managed to get both ranged strikers down the 200' drop into the stream below early in the encounter - the drow sorcerer made it back up (16th level At Will Dominant Winds) but the ranger, after getting about 120' back up on his flying carpet, got knocked back down to the bottom, but still ended up being pretty effective shooting up at long range with Twin Strike.
I failed in my attempt (as an eye tyrant) to use my TK ray to impale the dwarf fighter on a stalactite, and then the PC invoker did that to me instead - twice - using a slide effect from his zone of darkness and cold (Shadowdark Invocation; I resolved the stalactite as 2d8+8 and immoblised (SE), which seemed OK for a 17th level situational but multi-use option). But I did get to petrify one PC (the drow sorcerer) and at one stage had 3 or even 4 PCs taking ongoing 2d20 from my disintegrate ray (paladin, fighter, sorcerer and invoker - all very close together, but maybe only 3 overlapped at once).
Besides reinforcing my fondness for the tactical mobility that 4e generates, it also taught me that 4e beholders are pretty brutal (and play more like control than artillery - especially in combination with the terrain, a lot of action denial). The player of the fighter, in particular, got rather hosed in the fight - moving in close, and therefore vulnerable to the central eye, which is a vs Will attack that limits attacks to At Wills (his Will is not terrible, but his AC and Fort are both better). Which meant he didn't get to use some of his more funky immediate actions, and took a long time, and some effective use of cover while the beholder was trapped in the zone, to get off his close burst that also triggers AoE healing and thereby kept both himself and the invoker in the fight.
Anyway, I couldn't imagine running that fight to anything like the same effect in AD&D, 3E or any non-D&D fantasy system that I know.