Well, not quite as great.
The differences between Israeli Hebrew and Biblical Hebrew are: (1) tons of loanwords from European languages, (2) a pretty much complete abandonment of the Biblical Hebrew tense system and replacement with a modified tense system related to those of European languages and (3) a replacement of Biblical Hebrew's paratactic sentence structure with far more relative clauses and a completely different word order, basically the same sentence structure as English.
The two Hebrews sound much more alike than the two Englishes because most secular Hebrew speakers pronounce Biblical Hebrew and Modern Hebrew in the same way.
The Englishes sound radically different, because the correct ancient pronounciation has been meticulously reconstructed and pronouncing Old English like Modern English is never done.
Is that the guy who used to teach ancient Greek as a spoken language at MIT?
He was not one of the founders of the program, but it would not surprise me if he were one of the visiting professors.
True -- but wouldn't this make it harder for someone conversant with Biblical Hebrew to read modern Hebrew, rather than the other way aroud?
(2) a pretty much complete abandonment of the Biblical Hebrew tense system and replacement with a modified tense system related to those of European languages and
True, and it takes some getting used to. OTOH, the Hebrew verb is really simple in terms of number of forms. Biblical Hebrew has a perfect tense, roughly corresponding to past, and an imperfect, roughly corresponding to future (except when they mean the opposite!). What serves as the present tense in modern Hebrew is originally a sort of participial form, which still also serves as a participle and sometimes a substantive. Biblical Hebrew is far more likely to attach an enclitic for the direct object to the verb, but it's not unknown in modern Hebrew, just sort of "highbrow" on the whole, as is the use of attached possessives.
(3) a replacement of Biblical Hebrew's paratactic sentence structure with far more relative clauses and a completely different word order, basically the same sentence structure as English.
Sort of -- much less pronounced a difference in modern scholarly or literary writing (not to mention poetry) than in general conversational usage. And I learned to avoid a lot of errors in sentence structure (and sequence of tenses) by hearing Israelis' mistakes in English, assuming (turns out correctly) that they were mentally translating from Hebrew.
I don't think it adds up to a "different" language, though there's room to differ. As in "When is a dialect a language?"