I love Inform! and I'd still be using it, if it weren't for one main beef - it somehow manages to suck at math. There are no floating points available. How, during its entire development cycle, did this never come up as a needed or even slightly useful feature? I mean yeah, I could redesign my algorithm for skill decay and rust to use cabbages, but sometimes it can help to be able to get abstract, damnit!
I would say basic English skills are only tangentially related to learning Inform, however, in that the keywords and grammar looks like English, but if you try to talk to it about the weather in a way it doesn't like it will throw up its hands and call you a moron like any other language. It's a language full of "character" - as such, it can be difficult to debug or even understand what the hell is going on to start out with. Making it look like English, and sort of act like English, and coming up with documentation for common mistakes (the debugger reads like English too) took a lot of hard work, and that means that there's usually a very specific way the designers want you to say something so that it doesn't all fall apart around your ears.
That said, 90% of the appeal for me is still the anthropomorphism that weaves its way into the mix. Yeah, it's still a programming language, but you're writing sentences to make it do things. Once you get a flow going, assuming you're not trying to do something crazy at the time, it can be very much like writing a world into existence. If you struggle to relate to brackets and needlAbbrevnCamelFunctions and crap, you can get a taste of the intimacy experienced programmers have with their language using Inform. I got pretty far making a game before I realized how terrible it would be working around its lack of math, and I'd probably go back to it if they could just add some numbers. Maybe just one number? Doesn't even have to be a full float, you can use the back half for your garage. Please, Inform?