At first I was a little disappointed because I didn't think I'd enjoy putting together a bug list, but after reading through the codex I was pleasantly surprised by the design philosophy behind the army. Gone are the days of Nidzilla lists; 5th edition Tyranids are all about balance. Sure, you could still build a list centred around monstrous creatures, but the most effective lists will include a mix of small, medium, and large bugs.
The Core of the Army
Every good list needs a solid core to build around, and for me that was the Termagants and their bloated, hideous mother: the Tervigon. At 5 points per model your basic Termagant is cheap, and in squads of 20 or so they become pretty survivable, especially with all the cover saves in 5th edition. But each Termagant squad also lets you take a Tervigon as a Troop choice, and this is where things get interesting.
First of all, you get to take a 6 wound monstrous creature as a Troop choice! How awesome is that? But more importantly, the Tervigon both enhances your Termagants and spawns additional squads of the little guys from her horribly distended womb. With a couple cheap upgrades you're getting poisoned weapons and furious charge on all nearby Termagants, as well as counter attack and the potential to give feel no pain to one unit per turn. All of a sudden those 5 point Termagants are looking pretty impressive! I took two squads of Termagants and a Tervigon for my 1000 point match.
So now I had a solid core of scoring units to build my army around. What next? Anti-tank (AT) weapons!
A friend once described Tyranids with ranged weapons as bugs with bug-guns that shoot other bugs, and this is more or less true. Luckily, the Tyranids have some great AT bug-gunners, and the best of the lot has got to be the Hive Guard. For 50 points you get a T6 model with 2 wounds and a 2-shot, Str8 weapon that ignores most types of cover. What a bargain! I took a unit of 3.
The rest of the army was mostly personal taste: Genestealers to outflank and shred infantry, a Tyranid Prime to hunt independent characters and monstrous creatures (poisoned boneswords are pretty badass) and a Trygon Prime to wreak havoc in the enemy's backfield and draw fire away from my other units. All-in-all it was a fun list to build, and I ended up with a very balanced army with units that supported each other really well.
So my first Tyranid experience was a good one. The codex is effective without being overpowered, and allows for flexible list building. But I still don't think I'm ready to start a career in the service of the Hive Mind.