In my opinion Zapdos is a wonderful card, but it is outclassed by Tornadus in a ZPS(T) deck as it also resists the dreaded elephant, and helps you build up your secondairy attacker(s) (if wanted). Tornadus also 2HKO's the elephant, while Zapdos requires 4 heads to OHKO it, or an average of 2 heads per turn (-20 resistance and -20 from the body, meaning you need at least 160 damage with Zapdos to OHKO it if it's at 100% health).
In short, it has 10 more HP than Tornadus, and a more useful first attack, but that's where the good news ends. Of course Zapdos is also a basic, but that applies for Tornadus too, as well as the weakness and resistance stats of the cards. Tornadus has one less retreat, hits for more damage on a reliable way (sure, Zapdos has a higher damage cap, but is very less reliable!), and when you feel like it, you can charge your fellow pokémon as well.
So in my opinion Zapdos is a decent (but flippy) card to use that can either make a fun rogue deck (where I personally would take a basic ZPST deck, and swap the Zekrom for Zapdos, and throw in some Fliptini, and only for the lulz), or as a tech (where it can serve the role as a sniper, or as a risky OHKO'er). However, as long as Tornadus is available in modified, I don't think Zapdos deserves more room than maybe 1 in a ZPST deck as a tech.
When judging as a stand-alone card, I think Zapdos (when maybe combined with Kingdra prime or something of the likes) can make a pretty fun snipe deck which can easily KO evolving basics, wherever they are being build up. The 4x flip attack is never worth it in my opinion (even with Fliptini!) to rely on during a game.
If I were to rate it, I'd probably give it a rating of 2.3/5. 1 full point is given because it's a 120 HP basic, resists the type it usually is weak to (seeing most Lightning types), and sports a weakness that will usually OHKO it anyways when judging the current meta (Zekrom, Magnezone). Another point is given solely for it's first attack, as 50 snipe (at least unconditional) is pretty good, especially on a basic (even being a ''Legendary'' won't always help here, look at the CoL ''Legends'' for example). Then I give 0.3 points because the second attack has a high damage cap (even though it is unlikely), and because it is a decent enough starter (since it will hang around for a while mostly), as well as it's teching possibillity. 2 retreat (aren't Lightning types fast? And wasn't this a BIRD? guess that doesn't matter anymore in the TCG?) and expensive attacks hamper the card greatly, which immediately makes me drop 2 whole points, and the 0.7 drop is simply because of the ''luck factor'' you have with this card (for me that makes a -0.5 drop), and because it simply has nothing else to offer (for me a -0.2 drop).