I'm a pretty big fan of 8th edition, but there's one aspect of it that I can't stop thinking is completely broken. CANNONS! My problems with cannons are many, but these are the most glaring:
1. They are far too accurate. Since you know that the most you can roll on an artillery die is a 10, its just a simple matter of placing the marker 10" away from the back base edge of your target. They find their mark way more often than stone throwers.
2. They are far too powerful. I'm actually okay with them being S10, but their ability to do 6 Wounds in one shot makes them heinously good at killing monsters and other multi-wound entities.
3. They are way too cheap. They can often be purchased for under 100 points, which is ususally 2 or 3 times less than the targets they take out.
These three points combined to create the perfect storm of death that really hinders a lot of creativity in army lists. I have seen many a gamer begrudgingly pass up a cool centerpiece model because it will get shot to death by cannons. I, too, have often left my FW Verminlord at home because he'll just end up being a huge number of VP for my opponent when he hits it with a cannon.
So, I have a few solutions. Were any one of those 3 points to change, cannons would be in the perfect butter zone of dangerous, but not game-alteringly broken.
1. Here is my solution to make cannons less accurate, while still keeping the overall process of firing the cannon the same. After initially placing the marker, roll the Artillery die and a D6. If the D6 result is a 4+, move the cannon ball marker toward the target a number of inches shown on the Artillery die. If the D6 result is a 1-3, move the cannonball marker toward the cannon a number of inches shown on the D6.
This won't make the cannon horribly inaccurate, but will prevent firing a cannon becoming an exercise in using a tape measure for an (almost) guaranteed hit.
2. Instead of the cannon doing Multiple Wounds (D6), it instead does Multiple Wounds (D3+1). A wound range of 2-4 is still more powerful than other war machines, yet not so powerful that your much more expensive monster will be splattered by it in a single hit.
3. Simply increase the points of the cannon. I'd say anywhere from 150 - 200 would be a good range, since most targets that cost more than that will generally have some form of Ward save to protect them.
Now, mind you, i'm not suggesting all three of these changes be made. That would significantly underpower cannons. I think only one of these changes needs to be made, and I like option 1 the best out of all of them.