I think Ash's team would have been very different. Since he started with Squirtle instead, I think he'd still get Pikachu at some point, but the anime may have shifted a few thing that seem to be the norm so far. If Ash were to continue on to Johto, he may have left Squirtle (or at this point Blastoise) behind to start fresh with a Totodile, and as well may have left behind his entire party, rather then just 5 of them every saga. Bulbasaur and Charmander may have gone to Brock and Misty, or possibly two other reoccuring characters (who don't exist, but may have been created, such as Gary and the mysterious girl in the original opening)
I feel this would make for a much more diverse show. Ash could even change his clothes every generation to whatever the male lead of that area wears in the game. We could have an Ash that dresses like Jimmy (or whatever G/S kid's name is) an Ash that dresses like Brendan and finally an Ash that dresses like D/P's male lead. We could also see each generations electric pokemon enter a person's party, while in the current series they're relegated to filler pokemon at best.