Techmarine:
bad.
Anything that consumes your elite choices has to be very good, preferably at combat, while sticking to the marine fundamentals.
That's really the rule.
"So what about the techmarine?" people ask. If I were to say 'he's a horrible waste of time, points, and an elites slot,' not many would disagree.
But really, is he? Yes, he really is, but for completeness sake, we'll look at what he brings, and why he's so bad.
So, 50 points base. Default marine kit, only artificer armor instead of power armor. He gets all the expected skills and abilities, and like the master of the forge, he can repair things. Still a bad power, but it's there.
You also get 'bolster defence,' so in case you tool up for a table with a million terrain pieces in your deployment zone, you can build a 'badass' gunline with 3+ cover save for all.
Something is obviously wrong here, however. Look that profile.
One wound? Tactical marine statline? What happened, Ward? Old techmarine was too powerful, with his two wounds, and extra attack?
5o points for a tactical marine in artificer armor. Any invulnerable save? Nope. Any big guns included as default? No. Combat implements of doom? A single servo-arm.
Alright, so without extra stuff, techmarines are obviously horrible. Let's see what's available to bling him with. Pick one of stormbolter, combi-bolter, and plasmapistol. How nice. One useful gun (combi-melta.) What else? Pick a thunderhammer or a power weapon. On a guy with one attack, at 50 points base? No, thanks.