GTA 2 was top down as well.
It's also the best one. Only time Rockstar has ever successfully pulled off the style of gameplay they were going for.
As for the topic, yeah, GTA 4 is better than 5. It's got better shooting. The layout of gunfight sections the game has you enter during story missions is far better. The AI has a greater range of action in 4 (both during on-foot gunfights and car chases) which leads to more interesting situations in the openworld. Cars were better animated, and you had more control over them in 4. The enable to filp cars in 5 (without trying to flip them) removes the wrinkle of maybe needing to get into a firefight on foot while trying to steal a new car while the police or someone are after you, which means a whole set of gameplay opportunities simply disappear from the game. Five for some bizarre reason removes things like being able to pick random things off the ground to use as weapons, and the ability to crouch. I'd say the layout of the city in general was also just better in 4, if you were bored and just wanted to get into a big gunfight with the cops, it seems like there's more good places to do that in. You also use a lot more of the GTA4 map in general. Was also nice having a number of safe houses around the city, since their function for you the player is to help you lose the police.
The only really big problem GTA 4 had, outside of the problem of the third person shooting not being great (although it's better than any of the other 3D GTAs) and dropping all the stat stuff San Andreas introduced, was you're needy fucking friends calling you all the time to hang out and play somewhat half-assed mini-games. And that could've been made good my better writing, giving you some choice, and making the minigames a little better...most profitable games on the planet, you'd think they could up a little more effort into those mini-games than the Yakuza team does. Remember playing that Catherine a few years after GTA4 came out and thinking: Hey, this game as me hanging out with friends in a bar without making me wish the game would stop this.
Fives big problems are much worse than the problem four has. On top of everything it does worse gameplay wise, it never does fuckin' anything with any ideas it introduces. Trevor runs
Trevor Industries, his drug and firearms operation, and despite controlling Trevor you don't actually do jack shit with this. This could have been a big version of Dope War/Drugwars, throw in some Gangsters if you want to get deeper with it...instead nothing. There's also the heist stuff. The game has you recruiting all the people for heist missions, but instead of heist being this freeform things you can set up and pull off yourself they're just a tiny handful of pre-planned events. There's all these places around the city that could be used to set up your own heist, but the game does nothing with them. Like Trevor Industries around the end of the game it has movie lover Michael De Santa get to make movies like he's Chili Palmer. Only again this is just the game introducing something that could make for new interesting gameplay opportunities (especially since this is the endgame, and the game keeps going after you're finished despite there being nothing to do) and doing nothing with it. Franklin kind of seems to get this too in the form of his Tamagotchi dog you can't really do anything with (it being GTA I wonder if the original idea was more Digimon, then Michael Vick happened during development) and the bitch girlfriend that seems like maybe at one stage of development she was going to be some "make choices to see how that relationship goes" type thing, but they scrapped it and left the bitch line. There's also way too much boring driving to missions in GTA 5. There's too few places to go into, and most of the ones you can lock back up after their story usefulness is finished. And what the fuck is up with that useless casino being there? I'll take horse races and all manner of casino minigames over playing the GTA 5 stock market, which doesn't seem to quite work like it should.