Your question is a little ambiguous, but I'll try to answer it the best I can.
There are essentially three "versions" of Hyper-V. The first came out with the Windows Server 2008 product family, which is based on the Windows Vista kernel. The second version of Hyper-V came out with Windows Server 2008 R2.
In my opinion, I thought Hyper-V "v1" (2008) was good, but compared to VMware, you could see shortcomings aplenty. For a first version, Microsoft did a good job with Hyper-V. But VMware had been the key player in the market for years, and Hyper-V was going to have to earn its spurs.
Hyper-V "v2" -- the 2008 R2 edition of it, is a LOT more mature, and gives VMware a run for its money. With Virtual Machine Manager 2008 R2, administrators have a nice interface for easily moving virtual machines between hosts, changing hardware, managing virtual media, creating virtual media libraries, etc. Hyper-V earned its spurs. Hyper-V is definitely a worthy competitor to VMware, although I'm sure if you pushed Hyper-V and VMware hard in benchmarks and performance testing, VMware's experience and maturity would put it on top. Mind you, I'm saying this as a fan of Microsoft and I will happy stump for Hyper-V given the choice. However, to try looking at things and giving you a more unbiased viewpoint, I think VMware would still have the edge. It's got the edge on product maturity, and that's hard for competitors to overcome.
Hyper-V "v3" is coming with Windows Server 2012, and is also available in Windows 8. I personally have not used it. The machine upon which I have Windows 8 installed has a Core2 Quad processor, which is too old to support Hyper-V 2012 (it runs Hyper-V 2008 and 2008 R2 just fine).
Hyper-V 2012 requires second level address translation (SLAT), at least in the client (Windows 8) hypervisor, hence my comment regarding the Core2 Quad being too old. You need the newer generation (i.e. i3, i5, i7) processors.
Many hypervisor pundits are thinking that Hyper-V 2012 is a true competitor against VMware. If Hyper-V 2008 R2 didn't earn all of its spurs, there are many who think 2012 has earned those remaining spurs and is a worthy product to replace VMware.
Yes, hyper v is a virtual machine manager that ships with windows server 2008.
I have used it for some time and love it.
I however had some few issues with the networking:
1. managing the connectivity between multiple virtual machines and the host.
2. transferring files between virtual machines and the host.
I must have been doing something wrong.
I have had very pleasant experience with vmware regarding these issues.
I believe though that it's a strong competitor with vmware and with the constant improvement, it'll be worth implementing.