I'm not the perfect Guinea pig, as I have studied some very small amount of Greek already, but am happy to take the job.
My previous experience is that I worked through the first 5-6 lessons of Bluth's Koine program (listening to the words on headphones, and looking at pictures). I was very frustrated at the slow pace of progress and stopped.
I also did an hour a week of conversational Koine in an online course for ~24 weeks, last year. I was frustrated when it devolved into the instructor asking us to memorize grammar tables (in Greek, at least! I still know the greek word for Future tense; but I can't imagine using most of that information). I honestly could have continued with that, and probably would have learned those tables better than anyone in the class, (I'm very good at visual memorization), but I was so excited by the progress that we had made in the few conversational portions of the class that I was incredibly disappointed when we didn't keep it up. So I didn't bother with memorizing any tables and eventually dropped the class.
So, at the beginning of December, I had a working vocabulary of maybe 100 words, almost no knowledge of grammar (some verb and noun endings were familiar, but I couldn't produce them from memory). My pronunciation of written text was awful, and that frustrated me, because I had an idea of how things were supposed to sound. Texts were all "Greek to me!"
Some time in December, I started this interlinear approach. I can now read the first 5 chapters of Mark easily, the first three chapters of book one of Xenophon easily, the first half of the first chapter of Romans easily, and assorted poems and fragments that I have picked up. (The actual text, without any aids, dictionary or interlinear, etc.) I can look into just about any part of the NT and figure out what is going on, and I can read most parts of Mark and actually understand them. Xenophon is a bit harder to do that with. My pronunciation is far better (Modern Greek).
I think that my greater progress with the Koine mostly has to do with listening to Spiros Zodhiates' audio recordings of the NT that I have on CD. He uses a Modern Greek pronunciation (though he enunciates the accents well; I thought that wasn't a feature of Modern?). I have no knowledge of Modern Greek, but unless some of the recovered pronunciation Greek advocates come up with a pronunciation that sounds like a (beautiful) living language, I'll stick with it. Modified as necessary to make poetry work.
I also know the Bible reasonably well, which certainly helps. But I listen to the Zodhiates CD every day, often for hours, and would give almost anything for something similar for Xenophon. (Do we have any volunteers who are native speakers of modern Greek, know classical Greek, and want to make a quick $1,000?) On the other hand, my progress with Xenophon does seem to be picking up, so I hope to be at my current NT level in Xenophon by next month.
Regarding grammar: I am very good at memorizing tables, but that is a step towards a final goal; that final goal is internalizing a grammar. To internalize a grammar, you need to have a bunch of phrases that use that grammatical feature by heart. Your brain will then use those phrases as a template.
Now, having memorized a table of forms may get you a step closer to picking up the phrases and memorizing them as you come to them. So it's not completely wasted effort. But I think it's faster just to attack the phrases.
Here is something from Mark 4.
Βλέπετε τί ἀκούετε. ἐν ᾧ μέτρῳ μετρεῖτε μετρηθήσεται ὑμῖν καὶ προστεθήσεται ὑμῖν. ὃς γὰρ ἔχει, δοθήσεται αὐτῷ· καὶ ὃς οὐκ ἔχει, καὶ ⸀ὃ ἔχει ἀρθήσεται ἀπʼ αὐτοῦ.
I challenge anyone to remain ignorant of verb forms after learning sentences as visual and repetitive as the above.
I'm getting together with some of my friends tomorrow night for a "Greek night" (we're in the California Bay Area), and am very excited to have some community to practice with. One is a professor of classical Greek, and the others have all picked up a (very) small amount of Koine (through seminary, Bible camp, etc.). I have a tentative plan to go through the calling of the fisherman in Mark with everybody, teach everybody the vocabulary with charades and pictures, and if time permits, do the same with Sappho's 31st fragment. There is some great audio of it on YouTube from Kostas Katsouranis.
Also, I hope to have write some web tools that let me improve my interlinear approach. NT resources are good, but not perfect, and the Hamiltonian interlinear is not at all everything that I could wish for classical Greek.