|My Black Reach Terminators..That need to be re-based badly.|
I'm going to look at the shooty Terminators this time. You get 4 termies and the Sargeant in a standard squad. The sarge has a power weapon, which in 6th can be of any variety in the main rule book. The other 4 come with power fists and it's storm bolters all around. They're all veterans so they get 2 attacks each. The squad can go to 10 at double the price, and they can swap any fists for chain fists. For every 5 Terminators, the squad can take an assault cannon or heavy flamer that will replace a storm bolter or a cyclone missile launcher. At 10, they can also combat squad.
Back in 5th edition, these guys took a bit of a back seat to their Assault counterparts, but in 6th they've seen a resurgance and with good reason. They're a good fire base, a 2+ armor save goes a lot further then it used to now that most power weapons won't cut through it, and they're a mobile heavy weapon. I've seen a squad of 10 as Perdo Kantor's body guard, which was pretty nasty as Kantor gave them a third attack. The fact that they can both lay down fire, and do fairly well in a fight means they'll usually find use in an army. Since they have guns, having them walk is fine and with land raiders becoming a less attractive option in the new meta, a mob of 2+/5+ boots on the ground is never a bad thing. They're also good to park on an objective as a denial unit or to contest and between their armor and ATSKNF, they can hold up most things.
Now the bad...they aren't cheap. 5 models will cost as much as a tactical squad...and the financial cost has gone up. too since Black Reach is gone and the Dark Vengeance termies will need some work to not look like Dark Angels. While they're pretty sturdy and decent in a fight, they reflect the Marine standard of being good at lots of things, but not great at anything. Against a good dedicated assault unit, they're bound to struggle and with plasma getting more popular, they'll be easier to deal with at range. When their 2+ turns into a 5+, they die pretty quickly.
When running Terminators, they make a decent anchor for a battle line, or can hold down a flank. They're probably the only unit in the SM book that can actually perform in the shooting phase and the assault phase. They're not immortal, but used well, can survive a battle, or at least be a good destraction, drawing attention from your troops. They're a good unit that should be considered a great addition to any Space Marine army.