In my opinion:

Low level spellcasters are boring due to their lack of spell slots and rely on their companions to survive through to mid levels. At mid levels they are strong (but in my honest opinion only, are not as strong as people typically insinuate), and at high levels they are the gods they are supposed to be (if played by a decent player).

I really believe it boils down to spell choice and use of these spells as to how fun and effective a spell caster is.

I refer you to this. :P

This is really case of player tactics and personality. A perfect example is Meldair, the wizard in my live 3.5 campaign. All the way from level, he's been, if anything, a bane to my DM'ing existance lol. He knows how, when and where to use his spells. A good instance is that he's extremely capable with crowd control spells and always manages to have a perfect mix of spells for nearly any situation.

He's definitely a proven example that even a level 1 spellcaster is anything but weak in 3.5

And when his spell slots run dry or it's not safe to cast, he's always got a trusty hand crossbow ready!

I play pf and it seems they have ironed out some of the problems with 3.5 also alot of the 3rd party improvements make it almost an expansion. its helpful that its backwards compatible with 3.5 so really if u want to u can take what u like from each and do a homebrew

Ive played both 3.5 and pathfinder, and as a replacer DM when the other guys want a break, i prefer path finder. in 3.5, just a player saying "ok, i'm gonna grapple it!" made my brain hurt. now in path finder, its just 1 roll. nothing more. I love it. for the most part the classes havent changed much. multi-classeing really feels like its being penalized but it does solve the problem caused in 3.5, where everyone was half of at least 2 things and on top of that a whacked out splat book race with extra eyes or something. basically that was very hard to melt into the campaign role playing wise. like one game someone was a half minotaur, who the hell would have sex with a minotaur!? theyre basically angry walking cows. but anyway... my 2 cents, Pathfinder is an improvement. srry for the crazy run on sentences.

That's pretty much been my experience and opinion as well.

My only problem with Pathfinder, at least as its relates to these forums, is that there's rarely ever any moderate to high level campaigns for it. I enjoy really exploring the differences in characters and their class selections, and low level games are all so muddied to me in that regard. The whole X-times-per-day mechanic makes it that much worse for me, whether its the Vancian magic system or just a basic racial or class ability. At least at the 8th-15th level range (which I prefer) you have plenty of those things to choose from, rather than having to worry about actually running out of things to do in any given day.

But that's completely separate from the D&D vs. Pathfinder comparison. Pathfinder basically consolidated a lot of rules into simpler mechanics, kept things simple by reducing the benefits garnered by the embarrassing cheese of rampant multiclassing, and brought the core fantasy races back to the forefront. If anything, I wish all the optional races had some kind of penalty associated with them to make them more unattractive, too, but it's still a far cry better than the options in D&D. Every time I see someone ask about playing a Feral Necropolotian Dark Creature Half-Dragon Half-Fiend Half-Celestial Gelatinous Cube in an otherwise traditional campaign scenario, I just want to smack them and smack them hard. Doubly so when the DM replies with "sure!"

The problem with Pathfinder is that it adds stealth nerfs -- like to charging, or rogues, or tripping, or even grappling -- that aren't easily visible, but really mess up the competency of non-magical characters. And Non-magical characters did NOT need the nerf...

Like I said earlier: I would consider Pathfinder 3.55 (possibly just 3.51!), Trailblazer 3.60, and Legend 3.75. And other good options include using Mutants and Masterminds 2nd or 3rd edition to create dungeon-y classes. But pathfinder makes a bunch of senseless changes mixed in with the good ones, so it really is a wash to see whether it is actually BETTER than 3.5e. They are really, really the same.

Oh no, nerfs to charging, tripping, and grappling; or the three annoying things you're all but forced to do in D&D if you want to be a martial character. Whatever will they do now that other styles are equally viable? What a world, what a world...

Look at it this way:

COMPETENT
<Casting Characters>
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<Martial Characters with a useful schtick>
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<Martial Characters>
INCOMPETENT


What Pathfinder did was remove the 'martial characters with a useful schtick' from the game... the game is supposed to be more balanced, not less!

It's strange how I never seem to have these imaginary, hypothetical issues with any of the characters I play. I must be doing it wrong somehow. I lose at D&D. :'(