CQRS without Event Sourcing - what are the drawbacks?

I completely agree with Dennis, ES is no precondition for CQRS, in fact CQRS on its own is pretty easy to implement and has the potential to really simplify your design.

You can find a smooth introduction to it here

Secondly what benefits does CQRS on its own bring to the table?

• Simplifies your domain objects, by sucking out all the query concerns
• Makes code scalable, your queries are separated and can be easily tuned
• As you iterate over your product design you can add/remove/change individual commands/queries, instead of dealing with larger structures as a whole (e.g. entities, aggregates, modules).
• Commands and queries produce a well-known vocabulary to talk with domain experts. Other architectural patterns (e.g. pipes and filters, actors) use terms and concepts that may be harder to grasp by non-programmers.
• Limits the use of ORM (if you use one), I feel ORM's bring in unwarranted complexity if you try and use them for querying, the abstractions are leaky and heavy, trying to tune them is a nightmare :). Using an ORM only on the command side makes things much easier, plain old SQL is the best for queries, probably using a simple library to convert result sets into DTO's is the most you need.

More on how CQRS benefits design can be found here

Also do not forget about the non tangible benefits of CQRS

If you still have your doubts, you may want to read this

We currently use CQRS for projects with medium complexity and have found it be very suitable. We started out using a custom bootstrap code and have now moved on to using the Axon Framework to give us some of the infrastructure components

Feel free to PM me in case you want to know anything more specific.

Event Sourcing is optional and in most cases complicates things more than it helps if introduced too early. Especially when transitioning from a legacy architecture and even more when the team has no experience with CQRS.

Most of the advantages being attributed to ES can be obtained by storing your events in a simple Event Log. You don't have to drop your state-based persistence, (but in the long run you probably will, because at some point it will become the logical next step).

My recommendation: Simplicity is the key. Do one step at a time, especially when introducing such a dramatic paradigm shift. Start with simple CQRS, then introduce an Event Log when you (and your team) have become used to the new concepts. Then, if at all required, change your persistence to Event Sourcing and fire the DBA ;-)