Here are 10 to get you started.
- Apex is a proprietary language. Other than the force.com Eclipse plugin, there’s little to no tooling available such as refactoring, code analysis, etc.
- Apex was modeled on Java 5, which is considered to be lagging behind other languages, and without tooling (see #1), can be quite cumbersome.
- Deployment is still fairly manual with lots of gotchas and manual steps. This situation is slowly improving over time, but you’ll be disappointed if you’re used to having automated deployments.
- Apex lacks packages/namespaces. All of your classes, interfaces, etc. live in one folder on the server. This makes code much less organized and class/interface names necessarily long to avoid name clashes and to provide context. This is one of my biggest complaints, and I would not freely choose to build on force.com for this reason alone.
- The “force.com IDE”, aka force.com eclipse plugin, is incredibly slow. Saving any file, whether it be a class file, text file, etc., usually takes at least 5 seconds and sometimes up to 30 seconds depending on how many objects, data types, class files, etc. are in your org. Saving is also a blocking action, requiring not only compilation, but a full sync of your local project with the server. Orders of magnitude slower than Java or .NET.
- The online developer community does not seem very healthy. I’ve noticed lots of forum posts go unanswered or unsolved. I think this may have something to do with the forum software salesforce.com uses, which seems to suck pretty hard.
- The data access DSL in Apex leaves a lot to be desired. It’s not even remotely competitive with the likes of (N)Hibernate, JPA, etc.
- Developing an app on Apex/VisualForce is an exercise in governor limits engineering. Easily half of programmer time is spent trying to optimize to avoid the numerous governor limits and other gotchas like visualforce view state limits. It could be argued that if you write efficient code to begin with you won’t have this problem, which is true to an extent. However there are many times that you have valid reasons to make more than x queries in a session, or loop through more than x records, etc.
- The save->compile->run cycle is extremely slow, esp. when it involves zipping and uploading the entire static resource bundle just to do something like test a minor CSS or javascript change.
- In general, the pain of a young, fledgling platform without the benefits of it being open source. You have no way to validate and/or fix bugs in the platform. They say to post it to their IdeaExchange. Yeah, good luck with that.
Disclaimers/Disclosures: There are lots of benefits to a hosted platform such as force.com. Force.com does regularly enhance the platform. There are plenty of things about it I like. I make money building on force.com