Overall the army still feels very playable since the codex update. I have not experienced any downgrade in competitiveness or ability, if anything this has increased. A number of my units have become much cheaper, which for a Thousand Sons list is a major boost, and of course there are many more units and items I have been having fun with.
One particular favourite of mine is a Warpsmith with a Burning Brand of Skalathrax, which I have personally dubbed the 'dust-buster' pattern super-flamer, thanks to its shape. This weapon has never failed to kill something, and is virtually a no-brainer option for me when I do use the Warpsmith in my lists.
The character itself is very nice, with a good save, some nifty rules and a ton of attacks and wargear as standard. I've yet to really use his repair/curse abilities, since I've been mainly using him for offensive tactics; burning marines and accepting the challenges
The Mutilators are another fun addition that I've enjoyed playing, and of course modelling. With so many spare Terminators lying about, I thought it would be better to customise my own, than spend £31 on some new ones, even though the new ones look great (once the head issue is dealt with). Although they have a habit of dying to basic bolter fire, they can be very good at cutting up heavy units.
Daemon engines have been fun to explore. Having bought both a Forgefiend and a Helldrake, I've been thoroughly enjoying their destructive capabilities. Less so with the Helldrake, as one of the wings broke off, and I am yet to repair it (I hate to use part-built or damaged models in-game).
The pitfalls
I still feel that this first of the 6th edition codexes wasn't radical enough. Sure, we have a number of new units, and some units have improved (aka spawn), I and many others would have enjoyed much more in terms of variety and content.
For those who are wanting more, there is of course the option to look into Forgeworld's chaotic selection, which I strongly support; there are a number of great, fun, funny and awesome units within their many books (such as the Chaos Contemptor in IA:Apoc 2nd ed and the Storm Eagle in IA: Aeronautica).
One problem I've been noticing is the Sorcerer. Whilst he is excellent at dishing out spells, he is less than able in combat and challenges; the reduced wounds and combat skill has hit hard. Having said that, as discussed in a previous article, there are ways around this. I just perhaps need to experiment more with them and rid myself of my old frame of mind when using them.