Internet-scale BGP is a nightmare, and it's a miracle that it works so well. But what makes BGP so nightmarish in a private enterprise network? As a software engineer who pivoted to infrastructure, I find that BGP is a lot better than the series of proprietary link-level SLAs that it replaced.
I've always been partial to IS-IS for the IGP but I wouldn't say BGP is necessarily bad. Perhaps too many knobs and not exactly as speedy to react as you'd want for an IGP in all but basic topologies but both of those can be fixed by staying focused on tweaking a subset that makes sense. Also I think the whole iBGP vs eBGP thing drives people nuts.
IGPs (IS-IS, OSPF, EIGRP) and BGP solve different problems and networks often need both. Some niche networks get away with using only BGP (massive datacenters), and some get away with using only an IGP (smaller networks), and some don't even need that (small networks).
