The blizzard UI provides:
• A very obvious indication of of whether a mob is elite
• Resting/Level/Boss/Combat/Leader/Master Looter indicators (easy to do, but i'm listing things I like)
• Obvious reaction colors (hostile, tapped, neutral, etc)
• Threat indication around the frame by color.
• Castbar on target that doesn't just disappear the instant the cast finishes, and displays interrupted, border pulses green when the cast finishes successfully and whatnot.
• Buffs/Debuffs that are larger if you put the buff/debuff on them, as well as the gold radar thing mentioned earlier
• Non-distracting, non-animated frames.
• Debuff indicators on ToT
• Multiple rows of Debuffs/Buffs, that change position based on hostility of the unit (IE, if they're friendly, buffs appear on top, and debuffs below, and if hostile, the other way around. This makes it easy to look for a buff/debuff quickly)
• Buffs/Debuffs don't get covered by ToT as in _Neav
• Nice CP display around the frame.
• Solid combat feedback on the portrait frame.
I agree, though. They are ugly, which is my #1 complaint. Other than that, I've found that they are extremely solid, despite missing a druid mana bar (which I use DruidBar for) and a default 'nice' display for HP/power (which I use a modified version of CT_UF for).
As such, I've been working on and off on writing frames that mimic all of the functionality, but are more aesthetically pleasing. I wouldn't say it's especially close to achieving that goal at the moment, though.
