would you guys say this is an effective firewall script,
No, you need a whole lot more stuff. I'd go to:
...where you answer a bunch of questions, and it writes an IPTABLES or IPCHAINS firewall for you. Then you'll see what you're missing.
Sadly, you now need to ask the author for a password, but it's free.
But personally, I'd use IPCHAINS. It looks like you're not intending to do anything which would require IPTABLES, and IPCHAINS is simpler to configure.