As far as interfaces go, the default Gnome desktop is roughly identical to the previous version and is respectably Spartan, as befits a server operating system. However, a new install-time option now makes it easy to lay down the bare minimum of packages for a tighter, more secure server. For any admin who has waded through an RHEL install to remove buckets of spurious packages, this is a significant bonus.
One of the largest love/hate issues with RHEL has always been the RHN (Red Hat Network), which provides software update support for RHEL servers. On the one hand, RHN is a convenient way to control and schedule OS updates across a large number of deployed servers. On the other hand, it can occasionally impede simple tasks, which makes one yearn for the simplicity of open package repositories and Yum. For tightly controlled production systems, RHN provides a guaranteed package update and delivery mechanism, but working within its constraints can feel binding at times. Unfortunately, this doesn't change with RHEL 6.
Pay the cost to be the boss One last significant change in RHEL 6 is the pricing. The base pricing is similar to that of RHEL 5, but as you move up the chain, it gets much more expensive. The RHEL 5 entry-level server was $349, but that price included up to four virtual guests. RHEL 6 allows only a single virtual guest for the same money.
As you move up the support tier, prices increase. A single x86_64 license allowing four virtual guests with standard five-nines support will run $1,199, with 24/7 support hitting $1,949. For unlimited guests at the premium support level, expect to pay $3,249. RHEL 5 offered unlimited guest instances for a single price at the Advanced Server level. In short, it'll cost much more to run RHEL 6 as a virtualization platform.
Also, whereas RHEL 5 Advanced Server license costs covered an entire machine, it's limited to two CPU sockets in RHEL 6. There's no license for GFS2 in RHEL 6, while GFS was included in RHEL 5. It's possible to add GFS2 to RHEL 6, but it requires an additional license.
In fact, there are a pile of additional feature licenses, with the high-availability package costing $399 a year, load balancing $199 a year, and XFS support another $199 a year.
On the HPC side, Red Hat has broken out the costs of head nodes and compute nodes, which is a good idea. Head node add-on licenses start at $199 per year, with $29 per year licenses for compute nodes.
In addition to being the best Red Hat Enterprise Linux release to date, RHEL 6 is also the most expensive. As the pricing climbs, Red Hat may find that many customers have been using the OS long enough to seek out other alternatives -- or to turn to self-support, where they may have purchased support in the past. RHEL 6 is an attractive upgrade, but smaller shops especially will have to weigh the costs.