Out of curiosity, what are some of the SR4 rules you consider to be broken or ineffective?
Technomancer stealth in SR4 is broken beyond belief; threading in general can be extremely powerful, but technomancers threading high Level stealth are nigh undetectable by pretty much any node they choose to enter. Oh, and pornomancers (don't ask, but it's a thing...).
The Matrix in general, but not so much broken as it is complex. It's got a steep learning curve for everyone involved, and though it is easier than previous editions it is still harder than 5th (at least in terms of complexity; 5th still has it's share of issues with the Matrix...).
Summoning, which is just as broken in 5th unless the GM takes steps to address it (i.e. by using Edge for the spirits opposed test if of sufficient Force).
Chase combat, which again is also broken in SR5, and vehicle speeds in general.
All in all, there's a bunch of stuff that's mechanically unbalanced, and a few things that are just mechanically broken (i.e. barely works within the confines of the setting). But, and I think this is important enough for emphasis: nothing is so broken that it cannot be fixed with houserules. You just have to be willing to put in the effort is all, and that's the same across the board.
And I understand what you mean about the separation of rules and fiction in SR5. On my first couple reads I thought the game was horribly broken and missing a bunch of fundamentals. Then later I found a lot of them buried in paragraphs that looked like fluff. Still some stuff that looks incomplete, particularly in magic so that's why I'm asking how folks who've actually played the games felt they shook out.
Yeah, Street Grimoire got a lukewarm reception for good reason. I think it is my least favourite book of SR5 so far, followed closely by Data Trails, because they were both poorly edited (i.e. had sections of fiction and rules interspersed) and had game mechanics that were not particularly well implemented). A cardinal sin as far as I'm concerned is the utter lack of a proper table of contents, especially so when mechanics and fiction isn't properly separated making it even more time consuming to cross reference. It's not all bad, though, and it's definitely getting better. Run & Gun, Run Faster, Hard Targets, and Rigger 5.0 were all steps up as far as I'm concerned, though they all have their odd rules and editing issues. Still, I very much enjoy 5th Edition for what it is, so I hope you won't get too disparaged by what I consider a mere annoyance as opposed to an actual problem.
On a subject of particular interest to me, the ritual magic rules in SR5. I like the concept of expanding their use in the game and putting in ritual only spells, but the way they're written... they either seem to be taking a previously innate magician ability and making you now spend a starting spell pick to get them (wards, watchers) or very vague and/or underpowered. (Most other rituals.) Has anybody used ritual magic in your games? How did that go?
We tried, but it's no good if you've only got two magicians, really. It definitely seems like ritual magic, like blood magic, is a tool best left up to the GM for flavor. The effort it takes compared to the returns just isn't worth it in an average game session, and ritual magic can be quite time consuming in terms of in-game time which is something the GM has to plan for.
One thing I learned a long time ago is that how a game reads and how it plays can be two very different thing, and I'm very curious to hear what actual experiences have been like. 
Unfortunately, where Ritual Magic is concerned you read it right

Still, as far as I'm concerned you can't really go wrong with either edition of the game, to wrap back around. SR5 plays a little smoother so I'd honestly go for the later edition, warts and all, and if you need any gear from previous editions it's almost all simple enough to convert. As mentioned, we've got a house rule document that is pages upon pages and some of that is gear conversions, though most of it is rules clarifications and the like. So, jump right in!
