There should be categorization by intended use, such as 1st person shooter, MMORPG, RPG, RTS, etc etc. Its hard to tell what each engine is used for.
Most engines are more general than that. Very few of them can only be used for one game genre. I think this would add more clutter than useability.
an "in practice" list may be useful though. A list saying which games have used the engine in question, if any.