While probably very good at its time, it's not aged well at all:
-pokemon variety sucks, with random Johto pokemon such as the Mareep line randomly removed making it worse than G/S. Electric/Grass can be particularly difficult to find.
-To make things worse the variety of moves pokes learn is crap. Strongest grass move you can teach is Giga Drain which is bp 60 from post game.
-Johto pokemon still suck generally and can only be obtained post game
-Level curve is ass
-Most gym leaders don't even have Johto pokemon
-HGSS makes it completely redundant