It's been a while since I considered game series as a whole; I don't really have a favourite series because, in every series I have played, there has been at least one game that I've not enjoyed...usually more than one. The problem with considering a game series as a whole is that, whilst the better titles raise it up, the poorer titles drag it down. The likes of Final Fantasy, Tales, and even Pokemon have shown to me more than once that just because a game is part of a franchise does not mean that it is going to be any good.
I suppose the thing I appreciate the most about Pokemon is its consistency, though. Like most of Nintendo's mothership franchises, Pokemon has changed very little since its inception; it follows a core formula and deviates very little from that, adding and taking things away in an effort to produce an illusion of evolution in gameplay. That the fundamental gameplay hasn't been tampered with much over the years is fantastic, and I wish other developers would take note of this. Where you have Square Enix screwing with the ATB system and constantly trying to create a more action-oriented system, SEGA attempting to reinvent Sonic every few years to try and recapture his glory years, and Bandai Namco recycling the same set of tropes and locations over and over for new Tales titles, Pokemon sticks to a very basic, highly enjoyable formula and doesn't try to break the mould to the point that it becomes unrecognisable. I complain about it a lot at times - as do many others - but I can't imagine it any other way.
There is a Pokemon title in my Top 10 favourite video games - Platinum, specifically. So I suppose that's pretty good going for it. Of the six generations, the only ones I dislike are the third and the fifth, and I'm indifferent to the sixth. I loved the first, second, and fourth. So my impression is more favourable than not. This isn't even touching on the spinoffs, either.