I agree with @Michael, although here's my opinion.
Using either ADO.NET or EF (or Linq to SQL or NHibernate or anything else) nowadays comes down to a religious preference. There are differences in these frameworks, although they all are capable of doing what they do best.
As @Michael mentioned, some people do not like 'black boxes' and prefer doing it the way they want, so they know what is happening behind the scenes and gets more fine grained control. If you're happy to write your own framework, I'd say go for it. I personally like using a framework, because I'm not the only one using it, and it is widely tested, can get answers to my questions, and don't really have to test that framework so faster and easier development. On the other hand, if you hook up a SQL profiler, you'll see that there are quite a bit of noise in there and it is hard to track what's going on where as if you're using your own code, you'll know exactly why every single query is executed.
ADO.NET and EF are very feasible for cooperate applications. They are reliable and stable as they can get. (unless you're playing with a beta version.)
If you used Entity Framework, it worked well with your development, and you're happy about it, I do not see why you would suddenly move everything to ADO.NET (or any other framework).
It doesn't hurt to learn another framework, but your senior developer criticising your decision is not a reason to re-write your code. (Only thing that can come out of moving to another platform without a reason are bugs, stability issues and more bugs) As a wise man once said 'Don't fix it, if it ain't broken'.
If he says your code (or the framework of choice) is not reliable, ask him to prove it.
I use EF Code First, for my personal work, simply because it is faster development, and don't have to worry about how the database is created/managed. (Which I'm happy about, because I'm not a 'database guy', and happy to leave it as a ''black box. But your view may be different.)
About EF 5.
There are new additions as well as bug fixes coming to EF 5. you can have a look here for what's new. I think you need .NET 4.5 to run EF 5 beta. (Note: If you're trying out beta, expect bugs and 'reliability and stability issues', because .. well.. it's beta.)