We've had this discussion a lot and it took over the forums for a little bit when the news was still fresh. People just like them. They're pretty different from any other chapter.
i edited my previous post, but people posted negative things about ultramarines in the thread "why we love ultramarines". I dont want to start a flame war i just wanted an answer, and you gave me one
I can only speak for myself. I like them because they are a Knightly chapter, have no psykers, (I hate psykers ), They are scions of Sigismund my favourite Warhammer character, and they also have an Emperor Champion. They are a crusading chapter always taking the fight to the enemies of mankind with Zeal Faith and Fury! Also in TT the Squads composition is quite fun with Initiates and Neophytes forming to a 20 man squad! Also Land Raider Crusader Spearheads! And you gotta love the Tabards chains and lanterns bling they have! Also Close Combat!
As a templar fan and collector I will attempt to give you an answer. For me they are much more unique than the other chapters and just seem cooler. The whole Crusader in space theme helps a lot. They look great with many unique variants of armour pieces on the collection side. From a fluff side they are crusaders who see themselves as the Emperors chosen chapter (Champions dating back to Siege of Terra). And I love their style, always attack never defend, it is others job to defend BT push the eternal Crusade and if there is no offensive role for them in a campaign they don't take part. They are still continue the great crusade and are deffo the most bad ass close combat chapter( braces himself for hate ). They hold to Nikea as I believe because the emperoro didn't rescind it and are not afraid to speak their minds. They will insult other chapters and challenge the inquisition ( Saving the Celestial Lions/ having about 6000 members). PS did I mention they look like bad asses. That's pretty much my reasons, hope they help.
I share Fklm and Seth opinion, From me I would add that I like history and original templar chapter. Also BT fluff is different from all other chapters, when everybody defend we continue our eternal crusade and Sigisdmund is really bad ass.