ESXi 5 has many features like improved IOP handling, storage and network performance improvement, cluster HA architecture change, vMotion and SVMotion faster with VMFS5, VM memory and CPU support, Larger datastore support with less block size etc..
Host update utility is no more supported from vmware vsphere 4.x.. you can use host update utility to update from esx(i) 3.x to 4.. but from 4.0 to 4.1 its not supported.
If you feel free, can you share what did vmware support inform you, which made you not go with vmware vsphere 5. I can also think about it..