While writing about Spelunky, I made a rookie mistake: I failed to re-visit Spelunky Classic and give it a proper comparison to Spelunky HD - I only based my comparisons on 10-year old memories.
So I corrected my mistake, re-installed Classic and gave it a go. Things changed considerably, to the point that I feel I owe an apology to all of you.
Spelunky HD adds more than just fancy graphics and added difficulty: It also streamlines the controls. To open a container in Spelunky Classic you need to stand over it and press Up + Action, in Spelunky HD you only need to whip it, or cause it to break via other means. Classic has separate buttons for other uses (like a 'Purchase'-key) but HD does away with all of that. This is an improvement on HD's behalf. Also, HD allows you to whip items like rocks and such, but Classic does not. This matters if you're trying to push an item over the ledge to trigger a dart trap or have a heavy item clank someone below on the head.
The UI in Spelunky Classic is large, yet not intrusive. In HD it's all confined to the top left corner, but simultaneously blocks the view behind it, effectively creating a blind spot on the screen. This is not cool, some transparency would have gone a long way here.
Finally there's the minor issues I have with the Damsel. In Classic she stands there, makes a noise and a 'Help!'-speech bubble appears on-screen. So she has two visual indicators (red dress + speech bubble) and an aural indicator (which is only a generic sound) to help her get noticed. She also seems quite comfortable sitting in Indie's arms while being carried around, but when she runs around on her own she's visibly crying. All of these elements help establish sympathy in the player towards her, encouraging them to make the effort to rescue her.
In HD the speech bubble is removed, but her aural indicator is a proper 'Help!'-sound, and you can guess her location in-game by listening to where it's coming from. When picked up she literally acts like a concussed piece of meat, and when she runs around on her own there are no tears visible. This does not endear her so much to the player. I'm unsure why this was changed, but I honestly doubt it has anything to do with the game's options for what Damsel you want present: Female, Male, Pug or Sloth.
So looking back I change my numerical scores for both games: They both sit somewhere between 7.5 and 8, and which one is the better game just comes down to personal tastes. Spelunky HD deviates enough from Classic so that its additions and improvements fail to make up for it. IMO Classic still has the upper hand, but that's mainly because I can stomach the pixelated graphics and slightly bloated controls, I can perfectly understand others preferring the HD version.