Not in all aspects no, but as an actual game it was much superior. Reviews and fan reverence prove that
Was it, tho? Because the career, that is nowadays
somehow praised as engaging and well-structured, felt like an immense (and quite pointless) chore. The Autovista felt more like a licensed gimmick than an actual feature. The multiplayer was dreadful, with the public lobbies split in between car football (which, I'll admit, was fun in small doses) and impromptu sessions of car bowling (which
weren't), and private lobbies regularly splitting in two due to IP conflicts and desyncing. The car list was nothing to write home about in the end, the track list was padded to no end with fictional tracks that looked decent but were god-awful for racing (like Camino Viejo and Positano), the AI was just driving on splines and was dumb as a bag of bricks, and the menus weren't all that great (although they didn't require ten click-throughs to do the most basic things).
I've said it before and I'll say it again; what made FM4 so great for so many Forza enthusiasts was
the community surrounding it. I remember jumping into Forza around the time FM4 came out - I'd been a GT player before then, and Forza felt like a massive downgrade in many regards; that is, until I started to get involved with the Forza scene on the official forums and sunk countless hours playing the game socially, and then I got the point.
If that sense of community is gone, it's not just because of the faux-pas that was FM5 (which led many people to postpone or forego entirely buying a new Xbox), but also due to the the barriers to emergent gameplay imposed by the abandonment of many social features that came with that accursed game, and more broadly speaking, because of the death of this kind of environments on the internet. But of course, this won't stop people from looking at FM4 with rose-tinted glasses because they had a lot of fun playing with it, and will make claims as ludicrous as "the
paint booth in FM4 was better", "the public lobbies were
cleaner", "we had more race cars", and so on.