If so I'd have don't rather badly rather than getting a First - the UK system generally puts the emphasis on performance in the final year (or it least it did in ye olden tymes).
Generally, yes. There are some ostensibly harder courses you can take that are weighted slightly higher (the highest grade in an honors course may be a 5, while the highest in a normal course is a 4, so it contributes more to your overall GPA).
That said, I haven't ever really heard too many complaints about this system. In my experience the level of effort required from year to year is similar, it's the type of effort that changes. For example, in a first-year math course, you might struggle because you just don't know what you're doing. By a fourth-year math course, you may know what you're doing, you just have to do a lot more, and do it better.
One obvious complaint is that an engineering student might have 50% of their GPA attributable to non-engineering grades.
This is reduced a bit if you go to an engineering school. I only had to take 9 non-science classes (+ 4 gym classes).
That said, I think it's common to specifically point out your discipline-specific GPA (especially) if it is substantially better than your general GPA, whenever given the opportunity (like on a resume).