This is from a while back, actually, but back when I was still living in Okinawa I had started playing through Pokemon Crystal on emulator, and then had set aside for a few years, and a while ago (maybe the middle to end of last year?) I finally beat it (all of Johto and Kanto, but I didn't complete the Pokedex).
At the time, I didn't think I would have been able to get through it without a fast forward button.
But that said, it was really fun. It was similar enough to Red and Blue to satisfy that nostalgia, but it also, of course, had a lot more to it--more Pokemon, more gyms, more trainers, more features. I also noticed that it seems like it's possible to use a wider variety of Pokemon types from early on in the game; before even the second gym you can catch water types, a ghost type (Ghastly), psychic types, and rock types, whereas it seems like in the 1st gen. games it was all just normal, flying, and bug types in the wild for a while there.
In fact, I enjoyed this game so much that I actually started to play through it again . . . but I had a friend who wanted to play a video game together with me and we ended up playing Heart Gold and Soul Silver (I am playing Soul Silver, in Japanese).
Now, having experienced the DS version, I am pretty sure I never want to go back to the Game Boy version. The DS version just streamlines and gets rid of a lot things in the GB version that were just annoying, like getting rid of the limits to how many phone numbers you could record and how many items you could store in your pack and making PC box Pokemon strorage a lot easier to organize. For the GB version, I was thinking, "I couldn't make it through this game without a fast forward button," but the DS version does have a couple of things that are helpful in speeding things up, like the running shoes and the ability to turn off battle animations. So, grinding is still a chore, but not so much that I can't live without a fast forward button.
Some further thoughts:
I understand that with there now being a huge amount of different types of berries, it wouldn't be possible for a player to go around gathering them all from trees, but I can't get over my feeling that it is weird that berries don't grow on trees anymore and you have to buy them or exchange shards for them instead.
I also can't quite get over my disappointment that by the time it's possible to get a dragon type (Dratini) it's so late in the game that it's not very practical to level it up and use it in your team. Ice and dark types are also a bit difficult to get, though there are tons of Pokemon that can use ice and dark moves despite not being that type.
I'm really impressed by how deep you can go into this game if you want to. For example, when I was growing up playing Pokemon Red, I didn't bother with non-damaging moves whatsoever and just used leveling up and sheer brute force to win battles. Playing Pokemon as an adult, though, I find it really interesting how many different strategic things there are that you can do (for example, using Provoke to prevent that Miltank from going to sleep to recover its HP) and am enjoying trying to win battles using type strategies while my Pokemon are at a similar or sometimes slightly lower level than the gym leaders'. Besides that there are all the things you can do with Pokemon breeding, egg moves and so on, things that I mostly don't have time for but where you can do a lot of interesting things if you have the time and patience for it.
The games are really feature-rich, and even have a lot of new features that were not present in G/S/C. Some of these I am excited about, like having rematches with gym leaders. However, I find that I just cannot bring myself to care about completing certain sidequests like catching all of the unowns, or completing the Pokedex (way too much work).
Having someone to trade with is really awesome not only because of how much more rapidly you can increase your number of Pokedex entries but because of the ridiculously fast growth rate of Pokemon received in trades (150%!)
Having the first Pokemon in your party follow you around as a field sprite that you can talk to in order to see their reactions was also pretty fun, though more so when I first started playing (after that the novelty wore off).
The Pokewalker I can't comment on because I have a used copy of the game and the Pokewalker that came with my game isn't able to sync with the game for some reason.
Overall, this game is so fun that even though currently I have not finished going around and battling all the gym leaders in Kanto, I am already thinking about starting another playthrough, maybe a Nuzlocke or mono-type run.