You will get different answers to your question, as this is a subjective question and can be argued as well. Here is my take :
Why .Net is not preffered over java other than open source reason?
Ans - In real world, it is not 100% correct. JAVA is definitely preferred in some scenarios but not in all. e.g. In web application development, java is better. But microsoft is coming with some better things in asp.net as well. Like MVC3, JQuery etc. So it is just a matter of time that asp.net will be preferred technology for web applications as well. and for windows development you can not deny the fact that .NET is way better than JAVA.
Who is most powerful, java or .net?
Ans - As I said JAVA and .NET are both strong in their respective domain. e.g. For windows application development .NET has better tools and technologies available than that of JAVA. You can literally play with .NET to develop windows desktop application ranging from simple exe, Windows Service etc. JAVA is more powerful as of today in web domain. But microsoft is coming up with some really competitive things in .NET
What features .net has in comparison to java?
Ans : May be you can refer my previous answer for this question
Also you said for JAVA, open source is it's plus side. I can argue on that. In recent times, if you see there are lot more open source application coming in for .NET as well. e.g. Log4Net, NInject, NUnit, NLog, ITextSharp, File Helpers Library and lot more. Only the thing is Visual Studio (Editor for .NET) comes at a cost. But it is worth it. Developement is much more simplified.
Also there are lots of links on the net on .NET vs JAVA
1.
http://en.wikipedia.org/wiki/Comparison_of_the_Java_and_.NET_platforms[
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2.
http://www.computerworld.com/s/article/71221/.Net_vs._Java[
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3.
http://www.adam-bien.com/roller/abien/entry/java_ee_or_net_an[
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4.
http://stackoverflow.com/questions/1152194/net-vs-java-jobs[
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5.
http://www.youtube.com/verify_age?next_url=http%3A//www.youtube.com/watch%3Fv%3DH7QVITAWdBQ[
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Hope this helps.
All the best.
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